[3.0] demux: adaptive: fix bogus port discarding condition

(cherry picked from commit 6d65ec65)

On January 10, 2024, it was reported by John Cox jc@kynesim.co.uk on the vlc-devel mailing list that this is still an issue on 3.0. So backport the fix from 4.0.

added MRStatus::Reviewable label

changed milestone to %3.0.22

added Component::Demux: Adaptive label

added Version::3.0.x label

requested review from @fcartegnie

added MRStatus::WaitingForReviewerFeedback label and removed MRStatus::Reviewable label

approved this merge request