Codec Offload: Add NULL check as mCallbackThread is NULL
when offloaded HAL is running BLOCKING mode

b/14897952

Change-Id: I159a33e1181c1a62d80ab4bd3337a35dafaad884
Signed-off-by: Uday Gupta <guptau@broadcom.com>
Signed-off-by: Pierre Couillaud <pierre@broadcom.com>
Merge "Codec Offload: Add NULL check as mCallbackThread is NULL when offloaded HAL is running BLOCKING mode"
auto-merger: merge in from aosp/master

Conflicts:
	services/audioflinger/Threads.cpp