Orphan attachment's "parent_post" seems to be undefined or overflowed
In wp_posts (the db table), parent_post defaults to NULL. An ordinary post has no parent, and it's parent_post is set to 0 appropriately. Thus an orphaned uploaded file (not attached to any post) should also be set to 0, right?
What I find is that they are all set to a value like -1189551062, -1189547712, -1189551992 and so on, wich looks suspiciously like an overflow of some kind.
Looking at wp_upload_tab_upload_action() I notice that $post_id is never checked before constructing the attachment array. I don't know enough PHP/MySQL/WP to know if this might be the cause or not, but I need to know:
Are these (huge) negative post_parent id's a desired behaviour?
