gmod_src: Fixed IsValidModel sometimes returning true when t..

Revision 756
Fixed IsValidModel sometimes returning true when the model was loaded as an error.mdl Changed Files:
[ul]
[li]trunk/src_garrysmod/garrysmod/gmod_util.cpp[/li][/ul]

Committed By Garry Newman

Awesome,this has been bugging me for a while.