Fix stuttering in animation caused when animation plays too long without lastFrame set

Now we clamp the animation frames (first, last, current) between 0 and some reasonably large number 100,000.

This fixes the problem that would happen when the frame index reached a value that was so large that you could no longer represent fractions of frames (8,388,608). When the old code reached this value for a frame index, the frame index would no longer advance (because the delta in frame index would round to 0.0f).

By clamping the frame index values between 0 and 100,000 there is still a great deal of precision available for representing the fraction of the frame index (1/64th of a frame).

Tested as follows:
* set frame index to 99,900 and watched animation for 4 seconds as I rotate back and forth in the scene, and the animation did not stutter (other than the expected stutter as the animation rotates back to the 0 frame).