Guard mRearDisplayPendingOverrideRequest with mLock

mRearDisplayPendingOverrideRequest was null checked before acquiring the lock, which potentially caused the NullPointerException because the value might have changed while waiting on the lock.

Bug: 287264582
Change-Id: Ia14ca58a7d608ae95e1804dbcc5ab141f6f3b27c
Test: Manual
1 file changed