Fixed bug in ScrubberWidget
Fixed bug in ScrubberWidget

GridLayouts were not handled correctly by the widget causing
frames to be dropped.

basnijholt/holoviews,basnijholt/holoviews,mjabri/holoviews,ioam/holoviews,vascotenner/holoviews,ioam/holoviews,vascotenner/holoviews,basnijholt/holoviews,ioam/holoviews,mjabri/holoviews,vascotenner/holoviews,mjabri/holoviews