General: In the `is_countable()` polyfill, if the provided object implements `SimpleXMLElement` or `ResourceBundle`, consider it countable.

Props ayeshrajans, jrf, desrosj.
Merges [43220] to the 4.9 branch.
Fixes #43583.
Built from https://develop.svn.wordpress.org/branches/4.9@43221


git-svn-id: http://core.svn.wordpress.org/branches/4.9@43050 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/compat.php

@@ -512,7 +512,11 @@ if ( ! function_exists( 'is_countable' ) ) {
 	 * @return bool True if `$var` is countable, false otherwise.
 	 */
 	function is_countable( $var ) {
-		return ( is_array( $var ) || $var instanceof Countable );
+		return ( is_array( $var )
+			|| $var instanceof Countable
+			|| $var instanceof SimpleXMLElement
+			|| $var instanceof ResourceBundle
+		);
 	}
 }
 

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.9.6-beta1-43219';
+$wp_version = '4.9.6-beta1-43221';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.