Prevent integer overflow when processing covr MPEG4 atoms

If the 'chunk_data_size' value is SIZE_MAX, an integer overflow will occur
and cause an undersized buffer to be allocated. The following processing
then overfills the resulting memory and creates a potentially exploitable
condition. Ensure that integer overflow does not occur.

Bug: 20923261
(cherry picked from commit b5738ab0)

Conflicts:
	media/libstagefright/MPEG4Extractor.cpp

Change-Id: Id7fbe1f8543cd016cf5b272b7ea4cd1fb01f2b8f