The `update_active_strip_from_listbase()` function took meta-strips in
the "source" list into account, but didn't recurse into the
corresponding meta-strip of the "destination" list. This is now fixed.
`update_active_strip_from_listbase()` needed a few changes to resolve
the issue:
- It was renamed to `find_active_strip_from_listbase()` to limit its
reponsibility to just finding the active strip. It now leaves the
assignment to the caller. This reduces the number of parameters by 1
and makes recursion simpler.
- The destination strips are now, like the source strips, passed as
`ListBase`, so that both source & dest can be recursed simultaneously.
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