sequel of #7347
Play edited scene and Play custom scene didn't worked when main_run_args
hadn't $scene as argument.
Changes/Fixes the way how the editor handles scene paths when starting the
project/a scene
Play the project - no scene path
Play the edited scene - scene path of active scene in the editor
Play custom scene - scene path of custom scene
main_arg_runs is now empty by default and $scene won't be replaced
by the scene path anymore
Changed declaration if EditorRun::run, to remove a unused value
edd37eccd4