Changed based on code review to pull #657

Its possible that $variables['dc_array'] is an empty array which would
generate a warning. Just cleaning up this possible case.

theme/theme.inc

@@ -646,8 +646,10 @@ function islandora_preprocess_islandora_dublin_core_description(array &$variable
     }
   }
   $variables['dc_array'] = isset($dc_object) ? $dc_object->asArray() : array();
+  if (isset($variables['dc_array']['dc:description']['value'])) {
     $variables['dc_array']['dc:description']['value'] = nl2br(filter_xss($variables['dc_array']['dc:description']['value']));
   }
+}
 
 /**
  * Implements hook_preprocess().