Make SDL port QUIT events thread-safe
Make SDL port QUIT events thread-safe

sergiobenrocha2/mgba,MerryMage/mgba,MerryMage/mgba,askotx/mgba,sergiobenrocha2/mgba,Anty-Lemon/mgba,mgba-emu/mgba,cassos/mgba,libretro/mgba,fr500/mgba,Touched/mgba,Touched/mgba,zerofalcon/mgba,mgba-emu/mgba,matthewbauer/mgba,fr500/mgba,iracigt/mgba,Iniquitatis/mgba,Iniquitatis/mgba,Anty-Lemon/mgba,jeremyherbert/mgba,Anty-Lemon/mgba,cassos/mgba,askotx/mgba,iracigt/mgba,cassos/mgba,libretro/mgba,sergiobenrocha2/mgba,sergiobenrocha2/mgba,libretro/mgba,jeremyherbert/mgba,mgba-emu/mgba,iracigt/mgba,AdmiralCurtiss/mgba,fr500/mgba,askotx/mgba,AdmiralCurtiss/mgba,libretro/mgba,bentley/mgba,AdmiralCurtiss/mgba,nattthebear/mgba,MerryMage/mgba,sergiobenrocha2/mgba,libretro/mgba,Touched/mgba,Iniquitatis/mgba,matthewbauer/mgba,jeremyherbert/mgba,fr500/mgba,zerofalcon/mgba,mgba-emu/mgba,nattthebear/mgba,Iniquitatis/mgba,zerofalcon/mgba,jeremyherbert/mgba,askotx/mgba,Anty-Lemon/mgba,iracigt/mgba,bentley/mgba