Fix for issue #4235.

[AndrewDRX]

This PR:

• Fixes a bug

Description:
Fix for issue #4235 . The issue occurs due to the use of a NaN result produced from a zero denominator equation.

[photonstorm]

Thanks for your PR. While it fixes the problem, it feels like the wrong place to do it, as it's going to do this check every frame, for every tween, which doesn't seem worth it for something that can be caught and handled before the tween even starts playing (zero durations).

I think we ought to trap this in the Tween.play method.

[photonstorm]

Thanks for the PR but I've resolved this issue via capping the duration during the init of the Tween.