Fix Taskbar Background Visibility After Entering IME then Overview.

Fixed issue whereby taskbar background disappears as expected when the IME switcher is present, but does not appear again if the overview button is pressed after this state.

Flag: NONE
Test: Manually tested in Felix Landscape mode.
Bug: 297472865
Change-Id: If1074b28870c794db8a87dd6cd59f9656dc7c15d
(cherry picked from commit 5c34cf2d)