fix handling of invalid interval input

(similar to [SF#1102165] reported for date input)

Author: Alexander Smishlajev

roundup/cgi/templating.py

@@ -1510,7 +1510,7 @@ def __init__(self, client, classname, nodeid, prop, name, value,
             anonymous=0):
         HTMLProperty.__init__(self, client, classname, nodeid, prop,
             name, value, anonymous)
-        if self._value:
+        if self._value and not isinstance(self._value, (str, unicode)):
             self._value.setTranslator(self._client.translator)
 
     def plain(self):