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
Change-Id: I75cce323aec04a612e5a230ecd7c2077ce06035f
