Use the presence of manually set tax_base, not category_base, to determine...

Use the presence of manually set tax_base, not category_base, to determine whether tags use with_front to craft URLs. fixes #17308

git-svn-id: https://core.svn.wordpress.org/trunk@17789 1a063a9b-81f0-0310-95a4-ce76da25c4cd