AOD: Fix AOD background bug

There are certain conditions where the onDraw is still called
even though willNotDraw is set to true. Make sure we do not
draw the background then in ambient mode.

Change-Id: I63db1232434d9e8a80dc4c8a6dcacf726d8873ad
Fixes: 62090100
Test: receive notification / trigger ambient display, verify notification background is not showing