Prevent loading of nonexistant animations. Default to idling animation if existant.

Fixes a few issues with DroidWorks models, specifically an odd quirk (possibly due to the nature of the resources themselves since maps are generally very sloped which seems to play odd with the physics engine) which caused NPCs to jump at the game's start. Since most of the NPC's jump, crouch, turnleft and turnright behaviors were undefined, they would load a nonexistant animation and their parts would compress into a large 'blob'. This fix may or may not be a retroactive fix into DF2, although I have yet to see any issues that were similar to the ones with DroidWorks.