TinyMCE: fix image captions regexp when wpautop is disabled in wp_editor(). Fixes #29592 for trunk.
Built from https://develop.svn.wordpress.org/trunk@29730


git-svn-id: http://core.svn.wordpress.org/trunk@29504 1a063a9b-81f0-0310-95a4-ce76da25c4cd