Fix crash when starting daydream setting with wrong context

The context must be a UI context. This is a new requirement in P.

Change-Id: I3e2de5068f44010da7d57af030e9f029dd97a7f8
Merged-In: I28874f296da617f4cedf6706b0663b76671f1780
Fixes: 111375261
Fixes: 113312592
Test: robotests