[damned-lies] Prevent dictionary changed during iteration error

[Claude Paroz <claudep src gnome org>]

commit ea14a5e3dcb5431b01916a8aa7d75b67415eb12d
Author: Claude Paroz <claude 2xlibre net>
Date:   Sat Mar 25 11:47:46 2017 +0100

    Prevent dictionary changed during iteration error

 stats/forms.py |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/stats/forms.py b/stats/forms.py
index 71bf49a..f2a4932 100644
--- a/stats/forms.py
+++ b/stats/forms.py
@@ -57,7 +57,7 @@ class ModuleBranchForm(forms.Form):
 
     def clean(self):
         cleaned_data = super().clean()
-        for field_name in cleaned_data.keys():
+        for field_name in list(cleaned_data.keys()):
             if (field_name.endswith('_cat') and cleaned_data[field_name] is None
                     and cleaned_data[field_name[:-4]] is not None):
                 self.add_error(