LockscreenNotification: fix NullPointerException when i reboot

Log:

E/AndroidRuntime( 3640): java.lang.NullPointerException
E/AndroidRuntime( 3640): 	at
com.android.keyguard.KeyguardViewManager.inflateKeyguardView(KeyguardVie
wManager.java:401)
E/AndroidRuntime( 3640): 	at
com.android.keyguard.KeyguardViewManager.maybeCreateKeyguardLocked(Keygu
ardViewManager.java:383)
E/AndroidRuntime( 3640): 	at
com.android.keyguard.KeyguardViewManager.show(KeyguardViewManager.java:1
60)