Fix bug reported by Gabor Nagy in MultilinkHTMLProperty::sorted

from:

  https://sourceforge.net/p/roundup/mailman/message/37855862/

Author: rouilj

roundup/cgi/templating.py

@@ -2707,7 +2707,7 @@ def sorted(self, property, reverse=False, NoneFirst=False):
             return value
 
         # determine orderprop for property if property is a link or multilink
-        prop = self._db.getclass(self._classname).getprops()[property]
+        prop = self._db.getclass(self._prop.classname).getprops()[property]
         if type(prop) in [hyperdb.Link, hyperdb.Multilink]:
             orderprop = value[0]._db.getclass(prop.classname).orderprop()
             sort_by_link = True