VFS: Fix separatePath for the root directory
VFS: Fix separatePath for the root directory

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