File::processNew can return -1 which was not true for empty()

Also, File->getEnclosure() now throws exception if not enough metadata.

classes/File.php

@@ -364,16 +364,13 @@ class File extends Managed_DataObject
                 Event::handle('FileEnclosureMetadata', array($this, &$enclosure));
             }
         }
+        if (empty($enclosure->mimetype)) {
+            // This means we don't know what it is, so it can't be an enclosure!
+            throw new ServerException('Unknown enclosure mimetype, not enough metadata');
+        }
         return $enclosure;
     }
 
-    // quick back-compat hack, since there's still code using this
-    function isEnclosure()
-    {
-        $enclosure = $this->getEnclosure();
-        return !empty($enclosure);
-    }
-
     /**
      * Get the attachment's thumbnail record, if any.
      * Make sure you supply proper 'int' typed variables (or null).