There is no check for whether these supposedly redundant PPS
are actually redundant. One could check via memcmp which would
work in practice* (because all content buffers are initially
zero-allocated), but this is not portable as compilers may
trash padding inside structures as they wish.

In case the PPS is not really redundant the output is garbage.
This happens with several files from the FATE-suite. E.g.
h264-conformance/CVCANLMA2_Sony_C.jsv doesn't decode correctly
any more, whereas h264-conformance/CABA3_TOSHIBA_E.264 even
fails in ff_cbs_write_packet(), because the inferred value
of num_ref_idx_l0_active_minus1 mismatches with the value set
in the slice (this happens when num_ref_idx_l0_default_active_minus1
changes in the PPS; the value in the slice header is inferred from
the original PPS's num_ref_idx_l0_default_active_minus1).

*: Unless slice_group_id is used, i.e. unless slice_group_map_type
is six.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>