fix issue with destroy before rendering is complete
fix issue with destroy before rendering is complete

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