Allow scripter to play main()-less scripts without complaining

If a script is typed into the scripter window interactively and saved, scripter keeps a record of the file and automatically loads the script on the next run. When you press play on this auto-loaded script the runner module tries to load the module, then run it's main() method. However, an interactive script may not have a main method. Scripter should run main() if it's present, but fail silently if it is not present.

Not sure what to put here.
To trigger the initial bug Run krita, run scripter, create a script without main, save the script then press the play button.