fb: fix possible NPE on power key handling

fixes reported NPE which can cause SoD

E/InputManager-JNI(  805): An exception was thrown by callback 'interceptKeyBeforeQueueing'.
E/InputManager-JNI(  805): java.lang.NullPointerException
E/InputManager-JNI(  805):      at com.android.internal.policy.impl.PhoneWindowManager.interceptKeyBeforeQueueing(PhoneWindowManager.java:4185)
E/InputManager-JNI(  805):      at com.android.server.wm.InputMonitor.interceptKeyBeforeQueueing(InputMonitor.java:357)
E/InputManager-JNI(  805):      at com.android.server.input.InputManagerService.interceptKeyBeforeQueueing(InputManagerService.java:1351)
E/InputManager-JNI(  805):      at dalvik.system.NativeStart.run(Native Method)
E/InputManager-JNI(  805): An exception was thrown by callback 'interceptKeyBeforeQueueing'.
E/InputManager-JNI(  805): java.lang.NullPointerException
E/InputManager-JNI(  805):      at com.android.internal.policy.impl.PhoneWindowManager.interceptKeyBeforeQueueing(PhoneWindowManager.java:4185)

Change-Id: Ia0aa32c5472d0381d629a83492b42dec419b840e
Revert "Fix a bootloop problem when /data/system/usagestats/usage-history.xml is empty."

This reverts commit 286cba172e026515da98c08c93967a9c679ebba2.

AOSP just pushed 2 days ago a way better fix

Change-Id: Ib69ffad209b9f72857cf584c74cc1f8f74e6937a
Fix broken XML parsing idiom.

Code that expected a single top level element in an XML file
was doing something like :

while (type != START_TAG) { next(); }

This would loop forever when the XML being parsed was empty,
where each call to XmlPullParser.next() would return END_DOCUMENT.

bug: https://code.google.com/p/android/issues/detail?id=64173
Change-Id: I7543203e976a8999ae471a6c2d629249a87011bb