[1.0.X] Fixed `BaseFormSet.is_multipart()` so that it doesn't bomb when called on an empty formset.

Backport of [10073] from trunk.


git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@10075 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/forms/formsets.py

@@ -258,7 +258,7 @@ class BaseFormSet(StrAndUnicode):
         Returns True if the formset needs to be multipart-encrypted, i.e. it
         has FileInput. Otherwise, False.
         """
-        return self.forms[0].is_multipart()
+        return self.forms and self.forms[0].is_multipart()
 
     def _get_media(self):
         # All the forms on a FormSet are the same, so you only need to