Backport of "rtpbasepayload: Don't write header extensions if there's no corresponding..." into 1.20
requested to merge tpm/gstreamer:backport-mr-2198-into-1.20-rtpbasepayload-no-hdrext-without-input-buffer into 1.20
Backport of !2198 (merged) "rtpbasepayload: Don't write header extensions if there's no corresponding...".
Commits:
- fa070d20 rtpbasepayload: Don't write header extensions if there's no corresponding input buffer for the packet