Check version of savestates and allow to open another game when we are not in the main menu

First, when a savestate is loaded, it checks the git version and does not load when the version is different. It avoids crashes.
If it is not a good idea, we could add a parameter to ppsspp.ini to "Try to load savestate of other versions".

The second change allows to open another game when a game is being played or pause menu is being displayed.
The lines 179 and 180 of UI/EmuScreen.cpp may need to be reviewed, but I tested and it is working.