Hide the "Set Wallpaper" action bar when clicked.

This already happens everywhere except for the case where an external
app such as Photos started the wallpaper picker. So not only is this
more consistent, it also prevents crashes and other potential issues
caused by clicking "Set Wallpaper" too many times.

Bug: 25026717

Change-Id: I63c6a0ce68656e6e68094e88074a836d8c1034f9