No directory configuration for core (without rom) data

[guoyunhe]

Description

Related to bug libretro/libretro-2048#4

RetroArch's default save directory is only for roms. So when 2048 want to get save directory, it gets NULL and crash sometimes.

Expected behavior

RetroArch should provide a save directory for cores that don't work with ROMs.

Actual behavior

RetroArch provides NULL save directory to cores that don't work with ROMs.

Steps to reproduce the bug

1. Start RetroArch in terminal
2. Load 2048 core
3. Start 2048 core
4. Exit 2048 core
5. Check terminal output

You will see:

[2048] unable to save game data: Permission denied.

Game cores, like Craft, 2048, need to be tell the directory they store game data.

[andres-asm]

@fr500 tagging myself I may want to look at this