libstagefright: Check trackMeta for NULL

Add null-check for metadata returned by getTrackMetaData()
since it may return a nullptr

Author: Karthikeyan Periasamy <kperiasa@codeaurora.org>
CRs-Fixed: 1115425

Bug: 70919418
Test: TBD
Change-Id: Ic640b2dba815604fdeef1c546b17bfe5727c0dab
1 file changed