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
• On server: If the model isn't precached, if the model file doesn't exist on the disk
• If precache failed
• Model is the error model

Running this function will also precache the model.