Add braces around a conditional hook. This wasn't causing an issue as `if ( conditional ) /* multiline comment */ command();` is perfectly OK, but left open doubt and potential future bugs. See #25229


Built from https://develop.svn.wordpress.org/trunk@26509


git-svn-id: http://core.svn.wordpress.org/trunk@26403 1a063a9b-81f0-0310-95a4-ce76da25c4cd