Make sure we don't double-add -user or -network suffixes in...

Make sure we don't double-add -user or -network suffixes in convert_to_screen(). props SergeyBiryukov. fixes #16348


git-svn-id: https://core.svn.wordpress.org/trunk@17356 1a063a9b-81f0-0310-95a4-ce76da25c4cd