Frameworks/SystemUI: Hide expanded dialog when screen is off

Hide the expanded dialog while screen is off. Otherwise it
causes continuous buffer updates to SurfaceTexture
even when SCREEN is turned off and while In-Call causing a
spike in power consumtion. This fix ensures that the
power consumption is kept to a minimum in such a scenario.

CRs-Fixed: 339815

Change-Id: Ib9154528d4f88ba12ca234be7f929a61ed098be7