Undefined var breaks calls to http() with debug mode on

[benbalter]

When reseting $GLOBALS['wp']->main(), http() assumes there's a query, which throws an undefined var when there's not. Conditioned on isset() like used previously in the same funcion.

We'd still have to call $wp->main(), even without an argument. But the new runner now does this:

		if ( ! isset( $parts['query'] ) ) {
			$parts['query'] = '';
		}

So this is now fixed.