Merge pull request #578 from mjordan/ISLANDORA-1162

Address ISLANDORA-1162

islandora.module

@@ -1976,7 +1976,7 @@ function islandora_islandora_datastream_access($op, AbstractDatastream $datastre
     $hooks = islandora_invoke_hook_list(ISLANDORA_DERVIATIVE_CREATION_HOOK, $object->models, array($object));
     $hooks = islandora_filter_derivatives($hooks, array('force' => TRUE), $object);
     foreach ($hooks as $hook) {
-      if ($hook['destination_dsid'] == $datastream->id &&
+      if (isset($hook['destination_dsid']) && $hook['destination_dsid'] == $datastream->id &&
         (is_null($hook['source_dsid']) || islandora_datastream_access(ISLANDORA_VIEW_OBJECTS, $object[$hook['source_dsid']], $user))) {
         $applicable_hook = TRUE;
         break;