Checks if the specified model is valid.

A model is considered invalid in following cases:

• Starts with a space or maps
• Doesn't start with models
• Contains any of the following:
  • _gestures
  • _animations
  • _postures
  • _gst
  • _pst
  • _shd
  • _ss
  • _anm
  • .bsp
  • cs_fix
• If the model isn't precached on the server, AND if the model file doesn't exist on disk
• If precache failed
• Model is the error model

Running this function will also precache the model.