OpenGL: Minor gles2 fixes
OpenGL: Minor gles2 fixes

sergiobenrocha2/mgba,MerryMage/mgba,fr500/mgba,sergiobenrocha2/mgba,iracigt/mgba,mgba-emu/mgba,mgba-emu/mgba,AdmiralCurtiss/mgba,MerryMage/mgba,AdmiralCurtiss/mgba,fr500/mgba,sergiobenrocha2/mgba,Iniquitatis/mgba,sergiobenrocha2/mgba,fr500/mgba,mgba-emu/mgba,Touched/mgba,sergiobenrocha2/mgba,Touched/mgba,jeremyherbert/mgba,askotx/mgba,libretro/mgba,iracigt/mgba,MerryMage/mgba,Anty-Lemon/mgba,jeremyherbert/mgba,jeremyherbert/mgba,Iniquitatis/mgba,Touched/mgba,Iniquitatis/mgba,libretro/mgba,Anty-Lemon/mgba,Anty-Lemon/mgba,mgba-emu/mgba,fr500/mgba,askotx/mgba,iracigt/mgba,libretro/mgba,libretro/mgba,AdmiralCurtiss/mgba,askotx/mgba,Anty-Lemon/mgba,jeremyherbert/mgba,askotx/mgba,libretro/mgba,iracigt/mgba,Iniquitatis/mgba