Avoid an undefined variable notice. props sc0ttkclark. see #24236.

git-svn-id: http://core.svn.wordpress.org/trunk@24148 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Avoid an undefined variable notice. fixes #24236.

git-svn-id: http://core.svn.wordpress.org/trunk@24149 1a063a9b-81f0-0310-95a4-ce76da25c4cd