Fixes: [#18489] Adding (add filter) nested strips causes Blender VSE to segfault on frame render. [#18209] 3 VSE crash bugs with .blends (all left click and move mouse over Metastrip/Blend Mode related) ... and a new segfault I introduced with my last commit. Also: memcache limiter refcounts are tested now in critical places, printing an error message, since doing refcounting right is, well, hard.