only crop with 4 crop points

pandora/document/models.py

@@ -225,6 +225,7 @@ class Document(models.Model):
             if os.path.exists(src):
                 if size and page:
                     crop = map(int, page.split(','))
+                    if len(crop) == 4:
                         path = os.path.join(folder, '%s.jpg' % ','.join(map(str, crop)))
                         if not os.path.exists(path):
                             img = Image.open(src).crop(crop)