Comment 4 for bug 168417

I get Simon's result as well running [extensions-color-custom]. It's impossible to enter a formula with the 'live update' box checked because python's `eval()` breaks on incomplete stuff like 'r+'. I've attached a patch to swallow any exceptions and set the color to RED while the formula is invalid, in the hope that red is universally recognized as signal color. Also, eval is now guarded to prevent unwanted propagation of the python namespace into the function entry box. Tested with python2.6 on Ubuntu 10.4 amd64 and WinVista x86.

This is my first inkscape patch, I hope the diff works! I'm not sure how this is related to the original bug description. I think the only problem here is the `eval`.