Error in TaxonomyTerm source inner join

Problem

On line 41, where taxonomy_term_data (ttd) is joined with taxonomy_term_field_data (ttfd), there is a join with a criteria of ttd.vid = ttfd.vid. This is incorrect and should probably be tid.

$query->innerJoin('taxonomy_term_data', 't', 'tfd.vid = t.vid');

This (among other things) will cause the count method to return incorrect results, which in turn will make dependencies in migrations impossible, since taxonomy term migrations will always register as incomplete.

I will create a patch and submit.