Auto merge of #16950 - servo:warn, r=nox
Auto merge of #16950 - servo:warn, r=nox

Fix warning in a future compiler version.

(Do not upgrade yet because of https://github.com/rust-lang/rust/issues/42101)

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anthgur/servo,sadmansk/servo,fiji-flo/servo,thiagopnts/servo,jimberlage/servo,mattnenterprise/servo,avadacatavra/servo,peterjoel/servo,paulrouget/servo,anthgur/servo,rnestler/servo,mattnenterprise/servo,KiChjang/servo,DominoTree/servo,eddyb/servo,ConnorGBrewster/servo,emilio/servo,avadacatavra/servo,upsuper/servo,sadmansk/servo,notriddle/servo,fiji-flo/servo,splav/servo,dsandeephegde/servo,larsbergstrom/servo,dati91/servo,DominoTree/servo,nnethercote/servo,dati91/servo,KiChjang/servo,dati91/servo,saneyuki/servo,upsuper/servo,jimberlage/servo,pyfisch/servo,saneyuki/servo,emilio/servo,peterjoel/servo,splav/servo,cbrewster/servo,notriddle/servo,peterjoel/servo,anthgur/servo,eddyb/servo,canaltinova/servo,jimberlage/servo,upsuper/servo,DominoTree/servo,splav/servo,emilio/servo,rnestler/servo,pyfisch/servo,cbrewster/servo,dsandeephegde/servo,paulrouget/servo,ConnorGBrewster/servo,saneyuki/servo,emilio/servo,mbrubeck/servo,CJ8664/servo,sadmansk/servo,peterjoel/servo,larsbergstrom/servo,larsbergstrom/servo,SimonSapin/servo,DominoTree/servo,rnestler/servo,mattnenterprise/servo,KiChjang/servo,canaltinova/servo,fiji-flo/servo,notriddle/servo,szeged/servo,nnethercote/servo,paulrouget/servo,CJ8664/servo,thiagopnts/servo,KiChjang/servo,pyfisch/servo,CJ8664/servo,peterjoel/servo,SimonSapin/servo,jimberlage/servo,avadacatavra/servo,cbrewster/servo,upsuper/servo,ConnorGBrewster/servo,jimberlage/servo,KiChjang/servo,fiji-flo/servo,peterjoel/servo,larsbergstrom/servo,sadmansk/servo,mattnenterprise/servo,fiji-flo/servo,sadmansk/servo,eddyb/servo,larsbergstrom/servo,saneyuki/servo,paulrouget/servo,SimonSapin/servo,emilio/servo,dsandeephegde/servo,ConnorGBrewster/servo,peterjoel/servo,mattnenterprise/servo,nnethercote/servo,notriddle/servo,dsandeephegde/servo,thiagopnts/servo,saneyuki/servo,dati91/servo,anthgur/servo,paulrouget/servo,canaltinova/servo,peterjoel/servo,mattnenterprise/servo,canaltinova/servo,rnestler/servo,rnestler/servo,dsandeephegde/servo,CJ8664/servo,pyfisch/servo,saneyuki/servo,CJ8664/servo,DominoTree/servo,jimberlage/servo,pyfisch/servo,nnethercote/servo,peterjoel/servo,mbrubeck/servo,emilio/servo,emilio/servo,canaltinova/servo,mbrubeck/servo,KiChjang/servo,szeged/servo,DominoTree/servo,larsbergstrom/servo,szeged/servo,avadacatavra/servo,upsuper/servo,splav/servo,ConnorGBrewster/servo,splav/servo,upsuper/servo,paulrouget/servo,jimberlage/servo,eddyb/servo,pyfisch/servo,jimberlage/servo,DominoTree/servo,peterjoel/servo,paulrouget/servo,DominoTree/servo,mattnenterprise/servo,SimonSapin/servo,saneyuki/servo,dati91/servo,anthgur/servo,rnestler/servo,CJ8664/servo,canaltinova/servo,notriddle/servo,avadacatavra/servo,SimonSapin/servo,dsandeephegde/servo,paulrouget/servo,nnethercote/servo,larsbergstrom/servo,saneyuki/servo,notriddle/servo,upsuper/servo,anthgur/servo,DominoTree/servo,dsandeephegde/servo,thiagopnts/servo,mattnenterprise/servo,splav/servo,rnestler/servo,eddyb/servo,KiChjang/servo,CJ8664/servo,cbrewster/servo,szeged/servo,CJ8664/servo,nnethercote/servo,larsbergstrom/servo,upsuper/servo,paulrouget/servo,fiji-flo/servo,nnethercote/servo,szeged/servo,cbrewster/servo,nnethercote/servo,eddyb/servo,mbrubeck/servo,pyfisch/servo,eddyb/servo,rnestler/servo,splav/servo,pyfisch/servo,mbrubeck/servo,pyfisch/servo,SimonSapin/servo,szeged/servo,splav/servo,mbrubeck/servo,fiji-flo/servo,paulrouget/servo,fiji-flo/servo,larsbergstrom/servo,nnethercote/servo,KiChjang/servo,anthgur/servo,avadacatavra/servo,notriddle/servo,emilio/servo,saneyuki/servo,splav/servo,szeged/servo,ConnorGBrewster/servo,szeged/servo,sadmansk/servo,mbrubeck/servo,sadmansk/servo,szeged/servo,SimonSapin/servo,DominoTree/servo,thiagopnts/servo,dati91/servo,thiagopnts/servo,pyfisch/servo,jimberlage/servo,notriddle/servo,larsbergstrom/servo,emilio/servo,thiagopnts/servo,cbrewster/servo,ConnorGBrewster/servo,eddyb/servo,nnethercote/servo,dati91/servo,dati91/servo,cbrewster/servo,emilio/servo,szeged/servo,avadacatavra/servo,anthgur/servo,KiChjang/servo,mbrubeck/servo,notriddle/servo,canaltinova/servo,ConnorGBrewster/servo,cbrewster/servo,SimonSapin/servo,sadmansk/servo,saneyuki/servo,avadacatavra/servo,dsandeephegde/servo,thiagopnts/servo,splav/servo,KiChjang/servo,canaltinova/servo,notriddle/servo