Handle null buffer when calling Transaction::setBuffer

When Transaction::setBuffer is called with a null buffer, we release the
old buffer and unset the eBufferChange flag

Test: SurfaceControlTest
Test: ReleaseBufferCallbackTest#SetBuffer_OverwriteBuffersWithNull
Fixes: 233252754
Change-Id: I5cde94916655f82d146bd9d66c170b71db983966
2 files changed