allow iqm models without geometry

allow iqm models without geometry
allow iqm models without animation
compute model->surfmesh.isanimated and model->AnimateVertices in a
better way to make sure static models are identified as such (if bones
is 0 or 1, and no animation frames, treat as static)

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@11404 d7cf8633-e32d-0410-b094-e92efae38249