ListBox: Be more specific 'limit' values needing a cast.

Original code failed when 'limit' key is set to None.

product/ERP5Form/ListBox.py

@@ -2018,7 +2018,10 @@ class ListBoxRenderer:
 
     # Set the total number of objects.
     self.total_size = sum([s.object_list_len for s in report_section_list])
-    self.is_sample = self.total_size == int(param_dict.get('limit', -1))
+    limit = param_dict.get('limit')
+    if isintance(limit, basestring):
+      limit = int(limit)
+    self.is_sample = self.total_size == limit
 
     # Calculuate the start and the end offsets, and set the page numbers.
     if max_lines == 0: