Because SDL_SCANCODE_0 comes *after* SDL_SCANCODE_9 in the SDL keycode
table, we have to check if the keycode is between >=1 and <=0. We also
have to substract SDL_SCANCODE_1 in order to set command_parameter
properly.
Errata: Currently, the savestate created with CTRL+0 is created, but
refuses to load on Windows (working fine on Linux).