cgenius: Support for ROM arguments in shell files

[crcerror]

If no argument is parsed then the usual GUI from CGenius is launched. So this PR is a small enhancement and is usefull if you want to launch a single episode directly form PORTs menu or by a custom collection.

Usage:

#!/bin/sh
"/opt/retropie/supplementary/runcommand/runcommand.sh" 0 _PORT_ "cgenius" "games/[episode to launch]"

See: https://github.com/RetroPie/RetroPie-Setup/pull/2844 Thx @hhromic