With this header we can set a flag to signal that the whole buffer is
corrupt and should be ignored. With this we can cater to all cases:
* Window buffer fine, but cursor broken:
Use the spa_meta_cursor properties like id or offset accordingly
* Window buffer broken, but cursor fine:
Use the chunk flags
* Both are broken / the dequeued buffer is not usable
Use the spa_meta_header flag
Additionally clients can now check if a buffer contains spa_meta_header
data and can thus only check for the new or the old behaviour.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2516>
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