Don't re-hide the keyguard if it isn't showing.

This has a horrifying and unpredictable side effect of triggering
post-unlock Runnables that are stored in StatusBar.java, which can
result in a blank screen on unlock in certain race conditions.

Test: unlock, launch an app during the unlock animation, press power, wake up at bad time
Test: I wrote a custom build to force the above scenario to verify this works
Fixes: 214647311
Merged-In: I00655c2e85c46bd0c52b77094757e155b1a6f9c9
Change-Id: I9261ab9f04cc06db379676dccca72e452ece98d7