Since stone age of lib_query, the code would iterate over the current
list of active sequences (from a meta strip e.g.), and not over the
whole list of those.
This is a critical issue as it means in some cases (editing a meta strip
typically), some ID pointers would be missed/ignored by this foreach
looper, which is now at the center of most of our ID management code.
This caused a bug here at the studio, leading to loss of all sound IDs
used by sound strips when editing and undoing inside a meta strip, since
ID refcounting would not happen properly on strips using sounds outside
the meta-strip context during file reading of the undo steps.
To be backported to 2.83.
Differential Revision: https://developer.blender.org/D8671
ebf10b72b0