[3DS gPsp] : preserve rom's full filename with extension for saves

Hello retro coders,

I tested lastest gPsp retroarch version (1.8.5) on my new 3ds with cia version.
The result is astonishing ! Very good compatibility (but still some bugs on some roms)
But when I load a rom, the file created in "/retroarch/cores/savefiles" folder on the SDCard doesn't contain the filename with extension.
I explain :

1. I have a rom named as :
   "007 - NightFire (USA, Europe) (En,Fr,De).gba"
2. I create a zip containing this rom named as :
   "007 - NightFire (USA, Europe) (En,Fr,De).gba.zip"
3. I load the zip with gPsp
4. I save the state to slot 0 let's say.
5. I exit retroarch and go to see content in retroarch folders.

The result :
a)"/retroarch/cores/savefiles" : contains "007 - NightFire (USA, Europe) (En,Fr,De).sav"
b)"/retroarch/cores/savestates" : contains "007 - NightFire (USA, Europe) (En,Fr,De).gba.state"

The result b) is perfect. But the result a) is not correct and not conform to any other retroarch core's saves (snes9x, gambette, nestopia, genesis_plus_gx, etc.). The correct result should be, like others cores : "007 - NightFire (USA, Europe) (En,Fr,De).gba.sav"

This "problem" seems to be insignifiant, but I have at least ten cores. So ten cores writes to "/retroarch/cores/savefiles" and I like when I can filter the save thanks to its name (for exemple, I know that all ".gba.sav" are saves from gPsp. All ".psx.srm" are from pcsx_rearmed saves, all ".smc.srm" are from snes9x core saves, all ".gbc.srm" are from gambette saves (gameboy color)

This naming correction should be well appreciated.

Thanks.

Start by reproducing the save behavior with the gPsp core using a zipped ROM, then trace the code that creates files under /retroarch/cores/savefiles. Done means the save filename preserves the ROM's full .gba extension, matching the requested form while keeping savestate naming unchanged.