Fixed crash when tests are run without WAGTAILSEARCH_BACKENDS setting set
Fixed crash when tests are run without WAGTAILSEARCH_BACKENDS setting set

iansprice/wagtail,inonit/wagtail,quru/wagtail,davecranwell/wagtail,chrxr/wagtail,benemery/wagtail,Tivix/wagtail,darith27/wagtail,willcodefortea/wagtail,gasman/wagtail,marctc/wagtail,mephizzle/wagtail,gasman/wagtail,helenwarren/pied-wagtail,Tivix/wagtail,jorge-marques/wagtail,thenewguy/wagtail,lojack/wagtail,FlipperPA/wagtail,kurtrwall/wagtail,mikedingjan/wagtail,timorieber/wagtail,nrsimha/wagtail,Toshakins/wagtail,hanpama/wagtail,Klaudit/wagtail,stevenewey/wagtail,benjaoming/wagtail,inonit/wagtail,quru/wagtail,jordij/wagtail,jorge-marques/wagtail,benjaoming/wagtail,mikedingjan/wagtail,rsalmaso/wagtail,JoshBarr/wagtail,takeflight/wagtail,tangentlabs/wagtail,chimeno/wagtail,thenewguy/wagtail,nealtodd/wagtail,willcodefortea/wagtail,willcodefortea/wagtail,Tivix/wagtail,KimGlazebrook/wagtail-experiment,gasman/wagtail,zerolab/wagtail,taedori81/wagtail,wagtail/wagtail,mixxorz/wagtail,nimasmi/wagtail,nutztherookie/wagtail,mjec/wagtail,chimeno/wagtail,torchbox/wagtail,kaedroho/wagtail,Pennebaker/wagtail,nilnvoid/wagtail,Toshakins/wagtail,rjsproxy/wagtail,janusnic/wagtail,dresiu/wagtail,iansprice/wagtail,benemery/wagtail,chrxr/wagtail,Tivix/wagtail,mjec/wagtail,takeshineshiro/wagtail,m-sanders/wagtail,gogobook/wagtail,kaedroho/wagtail,benemery/wagtail,quru/wagtail,serzans/wagtail,JoshBarr/wagtail,nrsimha/wagtail,iansprice/wagtail,dresiu/wagtail,m-sanders/wagtail,takeshineshiro/wagtail,rsalmaso/wagtail,rv816/wagtail,hamsterbacke23/wagtail,rsalmaso/wagtail,JoshBarr/wagtail,jorge-marques/wagtail,rv816/wagtail,chrxr/wagtail,FlipperPA/wagtail,willcodefortea/wagtail,m-sanders/wagtail,Pennebaker/wagtail,lojack/wagtail,jordij/wagtail,rv816/wagtail,chimeno/wagtail,marctc/wagtail,WQuanfeng/wagtail,serzans/wagtail,darith27/wagtail,chimeno/wagtail,taedori81/wagtail,hanpama/wagtail,nealtodd/wagtail,iho/wagtail,mayapurmedia/wagtail,jordij/wagtail,zerolab/wagtail,hanpama/wagtail,100Shapes/wagtail,Pennebaker/wagtail,rjsproxy/wagtail,bjesus/wagtail,mixxorz/wagtail,wagtail/wagtail,janusnic/wagtail,hamsterbacke23/wagtail,serzans/wagtail,mayapurmedia/wagtail,helenwarren/pied-wagtail,mayapurmedia/wagtail,KimGlazebrook/wagtail-experiment,inonit/wagtail,mjec/wagtail,kaedroho/wagtail,Klaudit/wagtail,mephizzle/wagtail,benjaoming/wagtail,nimasmi/wagtail,thenewguy/wagtail,quru/wagtail,kurtw/wagtail,wagtail/wagtail,kurtrwall/wagtail,mayapurmedia/wagtail,davecranwell/wagtail,takeflight/wagtail,lojack/wagtail,nilnvoid/wagtail,jnns/wagtail,WQuanfeng/wagtail,stevenewey/wagtail,gogobook/wagtail,nrsimha/wagtail,zerolab/wagtail,Pennebaker/wagtail,takeflight/wagtail,FlipperPA/wagtail,jordij/wagtail,dresiu/wagtail,thenewguy/wagtail,darith27/wagtail,nimasmi/wagtail,mephizzle/wagtail,tangentlabs/wagtail,rjsproxy/wagtail,mixxorz/wagtail,torchbox/wagtail,davecranwell/wagtail,darith27/wagtail,hamsterbacke23/wagtail,iansprice/wagtail,nilnvoid/wagtail,Klaudit/wagtail,JoshBarr/wagtail,Klaudit/wagtail,iho/wagtail,iho/wagtail,m-sanders/wagtail,rsalmaso/wagtail,gogobook/wagtail,taedori81/wagtail,bjesus/wagtail,benjaoming/wagtail,KimGlazebrook/wagtail-experiment,kurtw/wagtail,jnns/wagtail,dresiu/wagtail,takeflight/wagtail,Toshakins/wagtail,iho/wagtail,thenewguy/wagtail,marctc/wagtail,gasman/wagtail,WQuanfeng/wagtail,tangentlabs/wagtail,jorge-marques/wagtail,zerolab/wagtail,kurtw/wagtail,bjesus/wagtail,kurtw/wagtail,stevenewey/wagtail,zerolab/wagtail,davecranwell/wagtail,kaedroho/wagtail,wagtail/wagtail,wagtail/wagtail,nealtodd/wagtail,janusnic/wagtail,100Shapes/wagtail,mjec/wagtail,gasman/wagtail,Toshakins/wagtail,nimasmi/wagtail,bjesus/wagtail,mixxorz/wagtail,timorieber/wagtail,takeshineshiro/wagtail,benemery/wagtail,jnns/wagtail,FlipperPA/wagtail,mikedingjan/wagtail,rsalmaso/wagtail,torchbox/wagtail,inonit/wagtail,chrxr/wagtail,hamsterbacke23/wagtail,takeshineshiro/wagtail,mixxorz/wagtail,nilnvoid/wagtail,kurtrwall/wagtail,jorge-marques/wagtail,stevenewey/wagtail,kurtrwall/wagtail,dresiu/wagtail,nutztherookie/wagtail,torchbox/wagtail,rv816/wagtail,taedori81/wagtail,hanpama/wagtail,nutztherookie/wagtail,nutztherookie/wagtail,mikedingjan/wagtail,nealtodd/wagtail,timorieber/wagtail,serzans/wagtail,taedori81/wagtail,helenwarren/pied-wagtail,tangentlabs/wagtail,jnns/wagtail,KimGlazebrook/wagtail-experiment,gogobook/wagtail,janusnic/wagtail,kaedroho/wagtail,nrsimha/wagtail,WQuanfeng/wagtail,rjsproxy/wagtail,marctc/wagtail,mephizzle/wagtail,100Shapes/wagtail,timorieber/wagtail,chimeno/wagtail