Prevent Warning

Error: Call to a member function getTimestamp() on boolean in islandora_view_datastream_cache_check()

includes/datastream.inc

@@ -161,6 +161,7 @@ function islandora_view_datastream_cache_check(AbstractDatastream $datastream) {
 
   if (isset($_SERVER['HTTP_IF_MODIFIED_SINCE'])) {
     $modified_since = DateTime::createFromFormat('D, d M Y H:i:s e', $_SERVER['HTTP_IF_MODIFIED_SINCE']);
+    if ($modified_since !== FALSE) {
       if ($datastream->createdDate->getTimestamp() - $modified_since->getTimestamp() > 0) {
         // Changed!
         return $return;
@@ -169,6 +170,7 @@ function islandora_view_datastream_cache_check(AbstractDatastream $datastream) {
         $return = 304;
       }
     }
+  }
   if ($return === 200 && isset($_SERVER['HTTP_IF_UNMODIFIED_SINCE'])) {
     $unmodified_since = DateTime::createFromFormat('D, d M Y H:i:s e', $_SERVER['HTTP_IF_UNMODIFIED_SINCE']);
     if ($datastream->createdDate->getTimestamp() !== $unmodified_since->getTimestamp()) {