keep custom command line parameters when unchecking

[Carl Paulino]

edit game. emulation tab. check 'use custom command line parameters' click ok. play game. now for testing or other reason, go back into edit game/emulation tab. uncheck 'use custom command line parameters' to disable it. doing this wipes out your setting. i would rather see the field retain what you had in there, so if you enable it again, you don't have to remember and retype what you had or make a change to it.