GBA BIOS: Fix some regressions regarding signed 16-bit loads (fixes #196)
GBA BIOS: Fix some regressions regarding signed 16-bit loads (fixes #196)

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