Fix animation frame duration issue

[xendke]

I've noticed that in my walking animation (a looping 2 frame animation) there's one frame being drawn more than the other. This PR fixes that.

It seems that there were a couple of instances of self.frameDuration that should have really been self.current.frameDuration

Before

After

[ericlewis]

Thanks for this fix — switching the reset sites to read self.current.frameDuration instead of the stale animation-level self.frameDuration is right, but I think the reset value needs one more change.

The advance check is (frameDurationCount - previousFrameDurationCount) >= self.current.frameDuration, and both counters are initialized to 1. At the loop/next-state sites frameDurationCount is reset to 1, so resetting previousFrameDurationCount to self.current.frameDuration makes the delta start negative: the first frame after a loop or state change displays for 2 × frameDuration − 1 ticks instead of frameDuration — a visible stutter on every loop whenever frameDuration > 1 (e.g. 5 ticks instead of 3 for a frameDuration of 3). In the next-state branch it also reads the outgoing state's frameDuration, since setState() only runs on the following line.

Since frameDurationCount goes back to 1, the consistent reset for previousFrameDurationCount is also 1 (the value both counters are initialized with):

self.frameDurationCount = 1
self.previousFrameDurationCount = 1

With that, the self.current.frameDuration = frameDuration assignment this PR adds in addState() is no longer needed — the state table constructor already sets it.