Fix for [#37362] Audio strips sometimes are evaluated incorrectly.

For details see bug comments. The problem was that blender's animation system didn't update the audio animation system anymore due to an optimization. Fixed this in a complex but proper way in the audio animation system, so that it can handle gaps of missing values.


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk@61239 954f8c5b-7b00-dc11-b283-0030488c597c