Coding Standards: Correct default parameter type in WP_Meta_Query::__construct().

This adjusts the default `$meta_query` parameter value to match the documented type of `array`.

Since the function is gated with a loose, falsey `! $meta_query` check, there is no difference to function behavior.

Follow-up to [17699].

Props justlevine.
See #63268.

git-svn-id: https://develop.svn.wordpress.org/trunk@60176 602fd350-edb4-49c9-b593-d223f7449a82

Author: SergeyBiryukov

src/wp-includes/class-wp-meta-query.php

@@ -165,7 +165,7 @@ class WP_Meta_Query {
 	 *     }
 	 * }
 	 */
-	public function __construct( $meta_query = false ) {
+	public function __construct( $meta_query = array() ) {
 		if ( ! $meta_query ) {
 			return;
 		}