Taxonomy postbox: fix toggling with "Choose from the most used tags" when...

Taxonomy postbox: fix toggling with "Choose from the most used tags" when several postboxes are shown, props SergeyBiryukov, fixes #23112 for trunk

git-svn-id: https://core.svn.wordpress.org/trunk@23278 1a063a9b-81f0-0310-95a4-ce76da25c4cd