Config doesn't output error message, when we have a required field (P…

…HP validation, not JS!).

This is the same fix as here: #3026, except that in the old pull request I've somehow screwed it up...

components/com_config/model/form.php

@@ -308,7 +308,7 @@ public function validate($form, $data, $group = null)
 			// Get the validation messages from the form.
 			foreach ($form->getErrors() as $message)
 			{
-				JFactory::getApplication()->enqueueMessage($message, 'error');
+				JFactory::getApplication()->enqueueMessage($message->getMessage(), 'error');
 			}
 
 			return false;