Fixed a bug when double tapping a notification in the normal shade

This fixes that sometimes holes where created when grabbing the panel while
closing the shade (eg. double tapping) or the notifications did not disappear.
It could also happen when using the clear all button.

Bug: 17969040
Bug: 17899136
Bug: 17961295
Bug: 17551216
Change-Id: Id7aa37bbcbae504039f90686e2bc364d18685205