Backport of "mpegdemux: Set duration on seeking query if possible" into 1.18
Backport of !1791 (merged) "mpegdemux: Set duration on seeking query if possible".
Commits:
- 7cec6449 mpegdemux: Set duration on seeking query if possible
Backport of !1791 (merged) "mpegdemux: Set duration on seeking query if possible".
Commits: