The "All Libraries" library didn't free its assets correctly on refresh,
so the asset previews didn't refresh correctly either. That's because it
didn't forward the removal request to the asset library that actually
owns the asset. It only freed assets from its own storage, which is
always empty.
This might make refreshing the all library feel a little slower, since
previews are now refreshed too. But in general this is fairly fast still
and there's an optimization to only load visible previews too.
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