When using WP_User::set_role() to set the role, don't unset all caps when the requested role matches the current role.

Props scribu, jammitch
fixes #18932


git-svn-id: http://core.svn.wordpress.org/trunk@22418 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/capabilities.php

@@ -797,12 +797,12 @@ class WP_User {
 	 * @param string $role Role name.
 	 */
 	function set_role( $role ) {
-		foreach ( (array) $this->roles as $oldrole )
-			unset( $this->caps[$oldrole] );
-
 		if ( 1 == count( $this->roles ) && $role == current( $this->roles ) )
 			return;
 
+		foreach ( (array) $this->roles as $oldrole )
+			unset( $this->caps[$oldrole] );
+
 		if ( !empty( $role ) ) {
 			$this->caps[$role] = true;
 			$this->roles = array( $role => true );