EntityModelManager::renderer: catch exceptions thrown by model()

[ericwa]

Fixes #1525
(both the crash when loading ad_quake.fgd in ad_magna.map, and the quoth flashlight example)

There is already a View::safeGetModel() function in ViewUtils but it takes a logger reference, which isn't desirable in this case:
EntityModelManager::model() already prints a warning to its logger if the model fails to load, so EntityModelManager::renderer() can just ignore and return NULL if model() throws an exception.

[kduske]

Thanks!