Don't ask to save empty nameless files

If you open and immediately close mousepad (without arguments), it shuts down immediately. If you open mousepad, type something, then close, it first asks if you would like to save the file. If you open, type something, undo to the start, and close, it shuts down immediately. If you open, type something, then delete everything, it first asks if you would like to save the file.

This is admittedly a very minor annoyance, but my primary use of mousepad is when I want to use it for a few seconds as, essentially, an extra clipboard. So it'd be nice if I could open it, paste one or two things, cut everything, then close without being prompted to save. I can't think of any use case where someone would want "ask me to save this empty unnamed file on closing" (if you want to create a particular new empty file, you'd probably rely on Save As, rather than "type something, delete it, close, select save").

It seems that forking is disabled for new accounts, so I can't file a PR, but I've attached a pretty simple patch that does this.