Prevent NPE in QuickQSPanel

When QuickQSPanel is recreated with the media player flag on, mHost is
null before it is set and will cause an NPE. The tiles will be set
correctly after the first time mHost is set.

Fixes: 146155011
Test: switch to Dark mode and see it doesn't crash.
Change-Id: Iacd23db46ec3b4ea026efc75da32f10f1edb1567