There is actually a valid (rare) case where a Library ID can have a `0`
versionfile value during blendfile loading: if that library only
contains 'indirect weak' linked data.
These IDs are only actually read in the library blendfile if they are
also used by some other data, otherwise they are purposedly dropped and
removed, and the library blendfile can end up never being read at all.
This would lead to a completely empty library on blendfile loading,
which can then be removed from the data-base.
NOTE: this _does not_ affect cases where the whole library is missing,
or some linked IDs from that library are not found anymore.
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