When parsing the main query, if `s` is set to empty: `?s=` and `$this->is_main_query() && array_key_exists( 's', $this->query )` - kill the query instead of loading the homepage. This will load the search page with no results.

Fixes #11330.


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git-svn-id: http://core.svn.wordpress.org/trunk@28436 1a063a9b-81f0-0310-95a4-ce76da25c4cd