FECUI_HandleEmuCommands was not re-entrant [fixes RANes crash on load savestate]

[Jamiras]

If any of the function calls invoked from FCEUI_HandleEmuCommands resulted in FCEUI_HandlEmuCommands being called again, the loop counter i would be updated by the nested call to NUM_EMU_CMDS, making the assignment at the end of the loop write past the end of the array. This results in memory corruption, and depending on what lied beyond the end of the array, could lead to crashing.

I've made i a local variable so a recursive call won't muck with it. The external function using i was modified to look at execcmd instead.