Prevent an offset error if the first menu item is a separator.

props phill_brown. fixes #23182

git-svn-id: http://core.svn.wordpress.org/trunk@24455 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Squash some PHP notices in taxonomy queries.

props hakre, wonderboymusic. fixes #16465.

git-svn-id: http://core.svn.wordpress.org/trunk@24456 1a063a9b-81f0-0310-95a4-ce76da25c4cd