_edit_attachments_query_helper does not properly preface table name when querying unattached media

[benbalter]

If a plugin modifies the media list on upload.php by joining wp_posts on itself (for example, to filter attachments which are children of a certain post type), MySQL throws an error when querying for unattached files because post_parent < 1 in _edit_attachments_query_helper is ambiguous without prefacing the table name (because of the join). All other columns in the query are explicitly named.

Steps to Reproduce:

1. Hook into posts_join_paged on upload.php and join wp_posts on itself ( e.g., JOIN wp_posts wp_posts2 ON wp_posts2.post_parent = wp_posts.ID)
2. Navigate to media upload and query for unattached media
3. Receive an error that post_parent is ambiguous

Preface table name

Example join filter to break upload.php (excluded media attached to pages)

Slightly cleaner, wrapped the string in double quotes

Can't see any downsides to this.

In [19720]:

Prefix table name against the post_parent field in _edit_attachments_query_helper() to avoid ambiguous queries. props benbalter. fixes #19779.