Backport of "v4l2videodec: Fix handling of initial gaps" into 1.22
requested to merge tpm/gstreamer:mr-4590-backport-into-1.22-forward-GAP-event-if-decoder-has-not-start-decoding into 1.22
Backport of !4590 (merged) "v4l2videodec: Fix handling of initial gaps".
Commits: