In `WP::handle_404()` introduce a filter `pre_handle_404` to short-circuit default header status handling.

This comes handy if you use WordPress without posts, means `$wp_query` contains no results.

Props prettyboymp, hakre, prettyboymp, Denis-de-Bernardy, ethitter, ocean90.
Fixes #10722.
Built from https://develop.svn.wordpress.org/trunk@36629


git-svn-id: http://core.svn.wordpress.org/trunk@36596 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/class-wp.php

@@ -629,6 +629,21 @@ class WP {
 	public function handle_404() {
 		global $wp_query;
 
+		/**
+		 * Filter whether to short-circuit default header status handling.
+		 *
+		 * Returning a non-false value from the filter will short-circuit the handling
+		 * and return early.
+		 *
+		 * @since 4.5.0
+		 *
+		 * @param bool     $preempt  Whether to short-circuit default header status handling. Default false.
+		 * @param WP_Query $wp_query WordPress Query object.
+		 */
+		if ( false !== apply_filters( 'pre_handle_404', false, $wp_query ) ) {
+			return;
+		}
+
 		// If we've already issued a 404, bail.
 		if ( is_404() )
 			return;

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.5-alpha-36628';
+$wp_version = '4.5-alpha-36629';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.