wp_get_attachment_thumb_url() back-compat with old format ".thumbnail" thumbnails broken

[DD32]

It appears that when using wp_get_attachment_thumb_url() for old attachments, Which use the "filename.thumbnail.jpg" format is broken, It cannot detect the thumbnail file, so returns a url to the fullsized image.

The bug is a 2-part:

1. The $id of the attachment wanted is not passed to wp_get_attachment_thumb_file()
2. The $thumb_file variable is not available in the 2nd part of the If at the time that PHP calls it, An extra compilation check needs to be done to make it available, Adding a set of brackets around it solves it.

[ryan]

(In [8257]) Fix wp_get_attachment_thumb_url() tumbnail back compat. Props DD32. fixes #7242