hevc: Check any change of SARs, colour descriptions and default display windows.
h264: Fix POC calculation when MMCO=5 is present.

After the decoding of the current picture and the processing of the memory
management control operations, the picture shall be inferred to have had
frame_num equal to 0 for all subsequent use in the decoding process, except as detection of the first VCL NAL unit of a primary coded picture.