#693 Buffer overflow

[Finn Thain]

There is an old crashing bug which I've been ignoring for ten years or so but finally got around to patching. It's easy to reproduce. Start nedit, select "Execute command line" from the "Shell" menu and click "OK". As I recall, doing that was always fatal for my i686-pc-linux-gnu builds on Gentoo/Linux. The problem is detected thanks to the stack smashing protector. It's caused (in part) by a bogus line number. Please see attached patch. The patch is not a complete solution but it does prevent the crash by use of a little defensive programming.