#379 avoid race condition caused by requestAnimationFrame
#379 avoid race condition caused by requestAnimationFrame

agamemnus/wavesurfer.js,ale-grosselle/wavesurfer.js,ale-grosselle/wavesurfer.js,agamemnus/wavesurfer.js,ffxsam/wavesurfer.js,katspaugh/wavesurfer.js,katspaugh/wavesurfer.js,ffxsam/wavesurfer.js