SystemUI: Fix NPE on creating taskview for controls ui

Fixes crash on launching A11 power menu with device controls.

Test
1) Set the power menu style to "Full (A11)".
2) Install the Google Home app.
3) Add your home to the device controls.
4) Long press the power button.

The power menu should open without crashing.

Change-Id: I6b7a96f75ef9b6b06491925a918122fdb2b0caad