subpicture: initialize the region picture with the region format

The region format has its own copy of the palette, whereas the source may have a temporary pointer.

This is working most of the time as the region format is usually used to get the palette of a region. But this makes the code potentially crashing if just the region picture is used.

The same problem exists in 3.0. But in 4.0 the picture palette is more prioritary than the region one since 1b5faa0f.

changed milestone to %4.0

added Component::Video: subpictures Status::BackportCandidate labels

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added MRStatus::Acceptable label and removed MRStatus::Reviewable label

The bottom line to this is that any picture created uses a shallow copy of the video format: https://code.videolan.org/videolan/vlc/-/blob/444d71bf2affe6146c951708f2065ab3baccdfe1/src/misc/picture.c#L214

This is fine 99.9% of the time. But it's not when the video format has a palette. There are no video_format_Clean() calls in picture.c either, for that reason. We might fix that.

mentioned in merge request !5060 (merged)

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• 0a87625d...dfd6d83e - 23 commits from branch videolan:master
• 33dd66bd - subpicture: initialize the region picture with the region format

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