Fixed a Wing3d crash related to Area Light - by trying to edit its property or saving the project Wings3d was crashing.

The bug was introduced when I tried to fix an issue related to unhiding adjacent faces with other material than default one (on mv/bugs1.5.pre1b - https://github.com/dgud/wings/commit/5ee5a9d89ab035fa2ed5a93412b55fb74ffbae5e)
Merge pull request #51 from Micheus/mv/bugs1.5.pre1d

Fixed area light crash