base: added NPE check for lockscreen see through and mPowerRequest

java.lang.NullPointerException
at com.android.server.power.DisplayPowerController.updateButtonLight(DisplayPowerController.java:1727)
at com.android.server.power.DisplayPowerController.setButtonTimout(DisplayPowerController.java:1796)
at com.android.server.power.PowerManagerService.updateUserActivitySummaryLocked(PowerManagerService.java:1404)

F/SystemServer(  711): BOOT FAILURE making Power Manager Service ready
F/SystemServer(  711): java.lang.NullPointerException
F/SystemServer(  711): 	at com.android.server.power.DisplayPowerController.requestPowerState(DisplayPowerController.java:786)
F/SystemServer(  711): 	at com.android.server.power.PowerManagerService.updateDisplayPowerStateLocked(PowerManagerService.java:1750)
F/SystemServer(  711): 	at com.android.server.power.PowerManagerService.updatePowerStateLocked(PowerManagerService.java:1193)

Change-Id: I4fba4a30ede28627e01e0ce4656a4d0d37f5bfd1