Destroy LayerBuffers before dropping them
Destroy LayerBuffers before dropping them

This should fix a potential pixmap leak and task failure when the LayerBuffer
is dropped (#1187).

aweinstock314/servo,RenaudParis/servo,michaelwu/servo,rixrix/servo,hyowon/servo,runarberg/servo,jimberlage/servo,brendandahl/servo,rentongzhang/servo,mattnenterprise/servo,nnethercote/servo,fiji-flo/servo,vks/servo,notriddle/servo,dvberkel/servo,dagnir/servo,j3parker/servo,upsuper/servo,jgraham/servo,kindersung/servo,splav/servo,steveklabnik/servo,jimberlage/servo,hyowon/servo,aidanhs/servo,avadacatavra/servo,notriddle/servo,AnthonyBroadCrawford/servo,DominoTree/servo,nick-thompson/servo,anthgur/servo,luniv/servo,bfrohs/servo,nnethercote/servo,juzer10/servo,pyfisch/servo,seanmonstar/servo,GreenRecycleBin/servo,wartman4404/servo,samfoo/servo,nerith/servo,nnethercote/servo,nick-thompson/servo,zentner-kyle/servo,aweinstock314/servo,samfoo/servo,mattnenterprise/servo,dvberkel/servo,DominoTree/servo,DominoTree/servo,zhangjunlei26/servo,ConnorGBrewster/servo,juzer10/servo,jimberlage/servo,ConnorGBrewster/servo,jlegendary/servo,notriddle/servo,rnestler/servo,anthgur/servo,jlegendary/servo,nerith/servo,pgonda/servo,anthgur/servo,karlito40/servo,froydnj/servo,rentongzhang/servo,notriddle/servo,bfrohs/servo,rnestler/servo,nnethercote/servo,KiChjang/servo,aweinstock314/servo,codemac/servo,dati91/servo,jimberlage/servo,ruud-v-a/servo,mbrubeck/servo,jdramani/servo,jdramani/servo,nnethercote/servo,tschneidereit/servo,mt2d2/servo,evilpie/servo,canaltinova/servo,AnthonyBroadCrawford/servo,chotchki/servo,ConnorGBrewster/servo,KiChjang/servo,tafia/servo,cbrewster/servo,rixrix/servo,avadacatavra/servo,avadacatavra/servo,aidanhs/servo,saneyuki/servo,cbrewster/servo,thiagopnts/servo,zhangjunlei26/servo,boghison/servo,peterjoel/servo,nnethercote/servo,KiChjang/servo,dhananjay92/servo,akosel/servo,fiji-flo/servo,larsbergstrom/servo,wpgallih/servo,aweinstock314/servo,s142857/servo,tafia/servo,dvberkel/servo,jimberlage/servo,rentongzhang/servo,notriddle/servo,mattnenterprise/servo,tafia/servo,huonw/servo,aidanhs/servo,steveklabnik/servo,mdibaiee/servo,splav/servo,AnthonyBroadCrawford/servo,luniv/servo,larsbergstrom/servo,mbrubeck/servo,boghison/servo,Shraddha512/servo,samfoo/servo,steveklabnik/servo,mdibaiee/servo,sadmansk/servo,zhangjunlei26/servo,splav/servo,nick-thompson/servo,wartman4404/servo,DominoTree/servo,kindersung/servo,jgraham/servo,s142857/servo,thiagopnts/servo,nnethercote/servo,dmarcos/servo,Adenilson/prototype-viewing-distance,GyrosOfWar/servo,dagnir/servo,caldwell/servo,karlito40/servo,dagnir/servo,walac/servo,indykish/servo,mt2d2/servo,mukilan/servo,szeged/servo,ryancanhelpyou/servo,youprofit/servo,GyrosOfWar/servo,jgraham/servo,jgraham/servo,seanmonstar/servo,aweinstock314/servo,szeged/servo,ryancanhelpyou/servo,jlegendary/servo,youprofit/servo,froydnj/servo,jgraham/servo,upsuper/servo,jimberlage/servo,seanmonstar/servo,hyowon/servo,cbrewster/servo,rnestler/servo,CJ8664/servo,Shraddha512/servo,mdibaiee/servo,splav/servo,vks/servo,chotchki/servo,mt2d2/servo,emilio/servo,shrenikgala/servo,SimonSapin/servo,deokjinkim/servo,A-deLuna/servo,sadmansk/servo,mukilan/servo,wartman4404/servo,eddyb/servo,sadmansk/servo,vks/servo,caldwell/servo,rixrix/servo,steveklabnik/servo,saneyuki/servo,GyrosOfWar/servo,tempbottle/servo,rixrix/servo,boghison/servo,rentongzhang/servo,paulrouget/servo,SimonSapin/servo,michaelwu/servo,akosel/servo,mt2d2/servo,canaltinova/servo,notriddle/servo,pyfisch/servo,seanmonstar/servo,jgraham/servo,dvberkel/servo,bjwbell/servo,aidanhs/servo,mdibaiee/servo,samfoo/servo,dsandeephegde/servo,jimberlage/servo,mdibaiee/servo,mbrubeck/servo,GyrosOfWar/servo,sadmansk/servo,zentner-kyle/servo,rnestler/servo,wartman4404/servo,shrenikgala/servo,dati91/servo,deokjinkim/servo,eddyb/servo,hyowon/servo,A-deLuna/servo,steveklabnik/servo,anthgur/servo,mattnenterprise/servo,szeged/servo,GreenRecycleBin/servo,splav/servo,KiChjang/servo,nnethercote/servo,indykish/servo,notriddle/servo,AnthonyBroadCrawford/servo,pyecs/servo,DominoTree/servo,mdibaiee/servo,rentongzhang/servo,youprofit/servo,zentner-kyle/servo,mbrubeck/servo,dhananjay92/servo,Shraddha512/servo,samfoo/servo,echochamber/servo,nrc/servo,ConnorGBrewster/servo,KiChjang/servo,larsbergstrom/servo,jimberlage/servo,froydnj/servo,echochamber/servo,evilpie/servo,zentner-kyle/servo,codemac/servo,szeged/servo,pyecs/servo,chotchki/servo,g-k/servo,upsuper/servo,eddyb/servo,szeged/servo,larsbergstrom/servo,shrenikgala/servo,froydnj/servo,canaltinova/servo,g-k/servo,pyecs/servo,huonw/servo,pyfisch/servo,zhangjunlei26/servo,peterjoel/servo,canaltinova/servo,luniv/servo,tafia/servo,paulrouget/servo,emilio/servo,pgonda/servo,SimonSapin/servo,WriterOfAlicrow/servo,ConnorGBrewster/servo,CJ8664/servo,zentner-kyle/servo,kindersung/servo,saratang/servo,nerith/servo,dvberkel/servo,saneyuki/servo,bjwbell/servo,AnthonyBroadCrawford/servo,ruud-v-a/servo,dhananjay92/servo,jlegendary/servo,peterjoel/servo,vks/servo,srbhklkrn/SERVOENGINE,emilio/servo,nrc/servo,boghison/servo,walac/servo,codemac/servo,runarberg/servo,hyowon/servo,luniv/servo,dsandeephegde/servo,mbrubeck/servo,rnestler/servo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