Database: Ensure that variables are defined correctly.

There were some cases where some local variables in `wpdb::init_charset()` could be undefined when they were used.

Props Frozzare.
Fixes #37683 for trunk.


Built from https://develop.svn.wordpress.org/trunk@38439


git-svn-id: http://core.svn.wordpress.org/trunk@38380 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.7-alpha-38438';
+$wp_version = '4.7-alpha-38439';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.

wp-includes/wp-db.php

@@ -734,6 +734,9 @@ class wpdb {
 	 * @since 3.1.0
 	 */
 	public function init_charset() {
+		$charset = '';
+		$collate = '';
+
 		if ( function_exists('is_multisite') && is_multisite() ) {
 			$charset = 'utf8';
 			if ( defined( 'DB_COLLATE' ) && DB_COLLATE ) {