Do not cancel screen brightness animation in forceUserActivityLocked unless screen is turning off.
Also not turn the screen on if PowerManager.preventScreenOn(false) is called while proximity sensor is active.
Fixes b/2254818 (dim display) where due to a race condition the screen is stuck in a dim state.
Change-Id: If6f805609c8d463631b9e22805e5242714ce34c0
Signed-off-by: Mike Lockwood <lockwood@android.com>