av1parse: Don't immediately reset timestamp in presence of TD
When a TD is being processed, it is not always pushed immediatly. Resetting the time information lead to lost of timestamp in TU to Frame conversion. The TU would be formed by buffer of [TD][Frame], and the timestamp taken from the TU buffer was lost then the TD was handled.
The handling of TS should be entirely done by the 3 functions:
- gst_av1_parse_handle_obu_to_obu() (direct input to output)
- gst_av1_parse_handle_to_big_align() Reset DTS on detected TU or TD
- gst_av1_parse_handle_to_small_and_equal_align() PTS on show frame, flat DTS
Fixes: 79312357
cc @bilboed
p.s. ideally some unit test are added.