configured better error detection around a missing xslt file

ObjectDetails.inc

@@ -87,10 +87,16 @@ function fedora_repository_object_details_XSLT($item) {
   $proc->setParameter('', 'baseUrl', $base_url);
   $proc->setParameter('', 'path', $base_url . '/' . $path);
   $input = NULL;
+
+  $xsl_file = './'. $path .'/'. variable_get('islandora_object_details_xslt_sheet', 'object_details_xslts/convertQDC.xsl');
+  // set an error message in case xslt parsing fails
+  $output = t("Failed to parse xslt file at @xsltFile", array('@xsltFile' => $xsl_file));
+  if (is_readable($xsl_file)) {
     $xsl = new DomDocument();
-  try {
-    $xsl->load('./'. $path .'/'. variable_get('islandora_object_details_xslt_sheet', 'object_details_xslts/convertQDC.xsl'));
     $input = new DomDocument();
+    try {
+      $xsl->load($xsl_file);
+
       $input->loadXML(trim($xmlstr));
     } catch (Exception $e) {
       watchdog('fedora_repository', "Problem loading XSL file: @e", array('@e' => $e->getMessage()), NULL, WATCHDOG_ERROR);
@@ -98,6 +104,7 @@ function fedora_repository_object_details_XSLT($item) {
     $xsl = $proc->importStylesheet($xsl);
     $newdom = $proc->transformToDoc($input);
     $output = $newdom->saveHTML();
+  }
   return $output;
 }