MediaPlayer: use local variable to check whether mTimeProvider is null.
MediaPlayer: use local variable to check whether mTimeProvider is null.

Bug: 18753807
Change-Id: I05ef22edea5d06b1efb1a01bf540404eb75ac954

xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base