Change InventoryUnit#backorderable_for_stock_item implementation
Change InventoryUnit#backorderable_for_stock_item implementation

Users were getting ActiveRecord::ReadOnlyRecord when updating a stock
item with backordered units. Due to ActiveRecored `joins` return
readonly objects

[Fixes #3066]

firman/spree,dandanwei/spree,omarsar/spree,bricesanchez/spree,raow/spree,sliaquat/spree,Ropeney/spree,tesserakt/clean_spree,knuepwebdev/FloatTubeRodHolders,Lostmyname/spree,madetech/spree,woboinc/spree,Hates/spree,ramkumar-kr/spree,pervino/solidus,keatonrow/spree,quentinuys/spree,zaeznet/spree,wolfieorama/spree,trigrass2/spree,bjornlinder/Spree,shaywood2/spree,kitwalker12/spree,hoanghiep90/spree,Senjai/spree,pervino/solidus,omarsar/spree,Kagetsuki/spree,gregoryrikson/spree-sample,cutefrank/spree,progsri/spree,lsirivong/spree,athal7/solidus,sideci-sample/sideci-sample-spree,assembledbrands/spree,ayb/spree,maybii/spree,JuandGirald/spree,bonobos/solidus,rbngzlv/spree,brchristian/spree,groundctrl/spree,Ropeney/spree,abhishekjain16/spree,vmatekole/spree,StemboltHQ/spree,piousbox/spree,locomotivapro/spree,cutefrank/spree,locomotivapro/spree,karlitxo/spree,PhoenixTeam/spree_phoenix,bricesanchez/spree,vinsol/spree,alejandromangione/spree,kewaunited/spree,pervino/spree,reinaris/spree,Engeltj/spree,omarsar/spree,vmatekole/spree,camelmasa/spree,pervino/spree,vinsol/spree,maybii/spree,jeffboulet/spree,vinayvinsol/spree,agient/agientstorefront,firman/spree,rbngzlv/spree,sunny2601/spree,edgward/spree,madetech/spree,rajeevriitm/spree,devilcoders/solidus,progsri/spree,sfcgeorge/spree,dafontaine/spree,NerdsvilleCEO/spree,pulkit21/spree,JuandGirald/spree,tomash/spree,Arpsara/solidus,lsirivong/spree,assembledbrands/spree,jimblesm/spree,archSeer/spree,shioyama/spree,jimblesm/spree,vinsol/spree,Kagetsuki/spree,sideci-sample/sideci-sample-spree,jspizziri/spree,derekluo/spree,jeffboulet/spree,devilcoders/solidus,JuandGirald/spree,yiqing95/spree,Mayvenn/spree,azclick/spree,CJMrozek/spree,Senjai/spree,trigrass2/spree,locomotivapro/spree,karlitxo/spree,nooysters/spree,volpejoaquin/spree,progsri/spree,xuewenfei/solidus,priyank-gupta/spree,vcavallo/spree,surfdome/spree,agient/agientstorefront,njerrywerry/spree,FadliKun/spree,sunny2601/spree,TrialGuides/spree,reidblomquist/spree,Senjai/spree,shaywood2/spree,njerrywerry/spree,berkes/spree,shioyama/spree,kewaunited/spree,dandanwei/spree,tailic/spree,maybii/spree,edgward/spree,Hates/spree,bricesanchez/spree,Senjai/solidus,bonobos/solidus,Engeltj/spree,robodisco/spree,firman/spree,watg/spree,DarkoP/spree,SadTreeFriends/spree,ckk-scratch/solidus,reinaris/spree,mleglise/spree,grzlus/solidus,dandanwei/spree,agient/agientstorefront,degica/spree,alvinjean/spree,Senjai/solidus,carlesjove/spree,keatonrow/spree,vinayvinsol/spree,locomotivapro/spree,APohio/spree,surfdome/spree,raow/spree,AgilTec/spree,lsirivong/solidus,assembledbrands/spree,azranel/spree,scottcrawford03/solidus,calvinl/spree,CJMrozek/spree,gregoryrikson/spree-sample,pulkit21/spree,Hates/spree,shekibobo/spree,knuepwebdev/FloatTubeRodHolders,hoanghiep90/spree,ckk-scratch/solidus,dandanwei/spree,Kagetsuki/spree,miyazawatomoka/spree,archSeer/spree,jsurdilla/solidus,CiscoCloud/spree,DarkoP/spree,Migweld/spree,jordan-brough/solidus,siddharth28/spree,joanblake/spree,thogg4/spree,TrialGuides/spree,lsirivong/solidus,hifly/spree,Arpsara/solidus,alejandromangione/spree,odk211/spree,vcavallo/spree,richardnuno/solidus,sfcgeorge/spree,zaeznet/spree,azclick/spree,DynamoMTL/spree,surfdome/spree,grzlus/spree,NerdsvilleCEO/spree,calvinl/spree,gregoryrikson/spree-sample,cutefrank/spree,brchristian/spree,TimurTarasenko/spree,forkata/solidus,forkata/solidus,njerrywerry/spree,hifly/spree,FadliKun/spree,azranel/spree,wolfieorama/spree,athal7/solidus,njerrywerry/spree,yushine/spree,tancnle/spree,alvinjean/spree,Engeltj/spree,AgilTec/spree,wolfieorama/spree,CJMrozek/spree,CiscoCloud/spree,miyazawatomoka/spree,scottcrawford03/solidus,azranel/spree,abhishekjain16/spree,siddharth28/spree,jeffboulet/spree,net2b/spree,alepore/spree,project-eutopia/spree,alvinjean/spree,keatonrow/spree,jhawthorn/spree,caiqinghua/spree,woboinc/spree,jaspreet21anand/spree,jparr/spree,biagidp/spree,watg/spree,Senjai/solidus,jasonfb/spree,DynamoMTL/spree,azranel/spree,net2b/spree,jordan-brough/solidus,miyazawatomoka/spree,thogg4/spree,beni55/spree,xuewenfei/solidus,mindvolt/spree,KMikhaylovCTG/spree,Machpowersystems/spree_mach,athal7/solidus,ahmetabdi/spree,robodisco/spree,devilcoders/solidus,odk211/spree,zaeznet/spree,AgilTec/spree,useiichi/spree,jimblesm/spree,grzlus/spree,scottcrawford03/solidus,freerunningtech/spree,edgward/spree,vinayvinsol/spree,richardnuno/solidus,builtbybuffalo/spree,beni55/spree,groundctrl/spree,groundctrl/spree,beni55/spree,vulk/spree,TrialGuides/spree,xuewenfei/solidus,adaddeo/spree,siddharth28/spree,Nevensoft/spree,lsirivong/spree,mleglise/spree,lyzxsc/spree,yomishra/pce,rajeevriitm/spree,camelmasa/spree,jspizziri/spree,welitonfreitas/spree,vmatekole/spree,net2b/spree,gregoryrikson/spree-sample,jordan-brough/spree,alejandromangione/spree,useiichi/spree,pulkit21/spree,rakibulislam/spree,adaddeo/spree,mindvolt/spree,softr8/spree,carlesjove/spree,carlesjove/spree,lyzxsc/spree,TimurTarasenko/spree,yiqing95/spree,volpejoaquin/spree,jsurdilla/solidus,sunny2601/spree,jparr/spree,Migweld/spree,shioyama/spree,ramkumar-kr/spree,surfdome/spree,tomash/spree,joanblake/spree,shekibobo/spree,vinayvinsol/spree,jparr/spree,beni55/spree,tesserakt/clean_spree,Arpsara/solidus,SadTreeFriends/spree,odk211/spree,grzlus/solidus,archSeer/spree,pjmj777/spree,Ropeney/spree,rakibulislam/spree,Kagetsuki/spree,abhishekjain16/spree,RatioClothing/spree,zamiang/spree,joanblake/spree,yushine/spree,grzlus/spree,orenf/spree,piousbox/spree,zamiang/spree,zamiang/spree,imella/spree,fahidnasir/spree,jordan-brough/spree,PhoenixTeam/spree_phoenix,yomishra/pce,builtbybuffalo/spree,vulk/spree,Migweld/spree,kewaunited/spree,FadliKun/spree,raow/spree,Machpowersystems/spree_mach,thogg4/spree,shaywood2/spree,welitonfreitas/spree,dafontaine/spree,Lostmyname/spree,quentinuys/spree,alepore/spree,fahidnasir/spree,edgward/spree,gautamsawhney/spree,moneyspyder/spree,radarseesradar/spree,softr8/spree,grzlus/solidus,vcavallo/spree,radarseesradar/spree,piousbox/spree,patdec/spree,alepore/spree,TimurTarasenko/spree,brchristian/spree,dotandbo/spree,reidblomquist/spree,vmatekole/spree,ckk-scratch/solidus,orenf/spree,ujai/spree,RatioClothing/spree,builtbybuffalo/spree,ujai/spree,imella/spree,camelmasa/spree,ckk-scratch/solidus,caiqinghua/spree,jaspreet21anand/spree,softr8/spree,cutefrank/spree,shekibobo/spree,jordan-brough/solidus,mleglise/spree,yushine/spree,abhishekjain16/spree,SadTreeFriends/spree,ahmetabdi/spree,urimikhli/spree,gautamsawhney/spree,moneyspyder/spree,jhawthorn/spree,CJMrozek/spree,sliaquat/spree,bonobos/solidus,Nevensoft/spree,hoanghiep90/spree,azclick/spree,hifly/spree,DynamoMTL/spree,net2b/spree,robodisco/spree,dotandbo/spree,APohio/spree,karlitxo/spree,patdec/spree,hoanghiep90/spree,dafontaine/spree,kitwalker12/spree,bjornlinder/Spree,lsirivong/solidus,reidblomquist/spree,siddharth28/spree,tomash/spree,pervino/solidus,CiscoCloud/spree,bjornlinder/Spree,JDutil/spree,richardnuno/solidus,ramkumar-kr/spree,volpejoaquin/spree,LBRapid/spree,yiqing95/spree,sideci-sample/sideci-sample-spree,pervino/spree,alejandromangione/spree,maybii/spree,tesserakt/clean_spree,Hawaiideveloper/shoppingcart,DarkoP/spree,forkata/solidus,builtbybuffalo/spree,raow/spree,watg/spree,StemboltHQ/spree,piousbox/spree,caiqinghua/spree,delphsoft/spree-store-ballchair,shekibobo/spree,JDutil/spree,camelmasa/spree,yomishra/pce,fahidnasir/spree,madetech/spree,Nevensoft/spree,grzlus/solidus,priyank-gupta/spree,knuepwebdev/FloatTubeRodHolders,patdec/spree,rakibulislam/spree,KMikhaylovCTG/spree,jhawthorn/spree,pulkit21/spree,tomash/spree,berkes/spree,DarkoP/spree,jeffboulet/spree,dafontaine/spree,Boomkat/spree,biagidp/spree,mleglise/spree,ayb/spree,rbngzlv/spree,radarseesradar/spree,calvinl/spree,nooysters/spree,ayb/spree,lsirivong/solidus,StemboltHQ/spree,APohio/spree,DynamoMTL/spree,pjmj777/spree,brchristian/spree,jimblesm/spree,nooysters/spree,athal7/solidus,jordan-brough/spree,alvinjean/spree,rajeevriitm/spree,wolfieorama/spree,scottcrawford03/solidus,project-eutopia/spree,APohio/spree,Lostmyname/spree,gautamsawhney/spree,sliaquat/spree,moneyspyder/spree,woboinc/spree,JDutil/spree,madetech/spree,calvinl/spree,tesserakt/clean_spree,urimikhli/spree,tailic/spree,Lostmyname/spree,rbngzlv/spree,zaeznet/spree,lyzxsc/spree,jsurdilla/solidus,lyzxsc/spree,project-eutopia/spree,CiscoCloud/spree,groundctrl/spree,tancnle/spree,FadliKun/spree,TimurTarasenko/spree,ujai/spree,delphsoft/spree-store-ballchair,Ropeney/spree,KMikhaylovCTG/spree,jparr/spree,degica/spree,freerunningtech/spree,JuandGirald/spree,reinaris/spree,orenf/spree,karlitxo/spree,mindvolt/spree,vulk/spree,lsirivong/spree,nooysters/spree,quentinuys/spree,NerdsvilleCEO/spree,priyank-gupta/spree,PhoenixTeam/spree_phoenix,PhoenixTeam/spree_phoenix,richardnuno/solidus,adaddeo/spree,progsri/spree,Engeltj/spree,quentinuys/spree,dotandbo/spree,rakibulislam/spree,hifly/spree,tailic/spree,vulk/spree,freerunningtech/spree,keatonrow/spree,miyazawatomoka/spree,Hawaiideveloper/shoppingcart,moneyspyder/spree,vinsol/spree,Machpowersystems/spree_mach,forkata/solidus,sfcgeorge/spree,berkes/spree,Boomkat/spree,ahmetabdi/spree,derekluo/spree,firman/spree,xuewenfei/solidus,caiqinghua/spree,priyank-gupta/spree,ramkumar-kr/spree,bonobos/solidus,jspizziri/spree,delphsoft/spree-store-ballchair,jasonfb/spree,derekluo/spree,kewaunited/spree,project-eutopia/spree,yiqing95/spree,Boomkat/spree,pervino/solidus,AgilTec/spree,grzlus/spree,LBRapid/spree,Hawaiideveloper/shoppingcart,thogg4/spree,jspizziri/spree,orenf/spree,patdec/spree,sliaquat/spree,Mayvenn/spree,zamiang/spree,agient/agientstorefront,pervino/spree,JDutil/spree,Migweld/spree,Senjai/solidus,delphsoft/spree-store-ballchair,devilcoders/solidus,tancnle/spree,carlesjove/spree,sunny2601/spree,biagidp/spree,Mayvenn/spree,yushine/spree,KMikhaylovCTG/spree,adaddeo/spree,NerdsvilleCEO/spree,archSeer/spree,ayb/spree,TrialGuides/spree,trigrass2/spree,useiichi/spree,Boomkat/spree,RatioClothing/spree,fahidnasir/spree,robodisco/spree,reinaris/spree,trigrass2/spree,Hawaiideveloper/shoppingcart,Nevensoft/spree,rajeevriitm/spree,omarsar/spree,Hates/spree,shaywood2/spree,volpejoaquin/spree,jasonfb/spree,softr8/spree,SadTreeFriends/spree,radarseesradar/spree,joanblake/spree,vcavallo/spree,tancnle/spree,sfcgeorge/spree,jordan-brough/solidus,jsurdilla/solidus,imella/spree,mindvolt/spree,welitonfreitas/spree,LBRapid/spree,azclick/spree,odk211/spree,ahmetabdi/spree,Arpsara/solidus,gautamsawhney/spree,degica/spree,berkes/spree,urimikhli/spree,kitwalker12/spree,jaspreet21anand/spree,welitonfreitas/spree,pjmj777/spree,reidblomquist/spree,useiichi/spree,jasonfb/spree,Mayvenn/spree,dotandbo/spree,derekluo/spree,jaspreet21anand/spree