Reset our status bar window fade color on screen off.

Previously, turning the screen off with the panel expanded would
run one time through panelExpansionChanged, leaving the background
in an intermediate state.

This has probably been around for a while, only uncovered now
that we can see it (if the status bar is translucent).

Bug:11357145
Change-Id: I55b768696c8791f82265a61d2c0f665503ad8bb0