Following [38625], any media searches that already included JOINs,
e.g., `tax_queries`, would get trampled when we joined the post meta
table to search for filenames. This preserves existing JOINs and
also only applies the `_filter_query_attachment_filenames()` filter
when a search query is being performed.
Props flixos90, joemcgill.
Fixes#22744.
git-svn-id: https://develop.svn.wordpress.org/trunk@38733 602fd350-edb4-49c9-b593-d223f7449a82
2eade6230d