Fix PHP notice in `WP_Tax_Query::get_sql_for_clause()`.

Previously, the `$where` variable was not initialized, so that when an invalid
'operator' was passed, PHP would complain that `$where` was undefined.

Props dlh.
Fixes #32756.
Built from https://develop.svn.wordpress.org/trunk@32910


git-svn-id: http://core.svn.wordpress.org/trunk@32881 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/taxonomy.php

@@ -1046,7 +1046,7 @@ class WP_Tax_Query {
 			'join'  => array(),
 		);
 
-		$join = '';
+		$join = $where = '';
 
 		$this->clean_query( $clause );
 

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.3-alpha-32909';
+$wp_version = '4.3-alpha-32910';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.