Silently ignore subscriptions that already exist

Instead of IntegrityError

maillists/management/commands/import_mailling_list.py

@@ -60,7 +60,9 @@ class Command(BaseCommand):
     def _iter_emails(filename):
         with open(filename) as f:
             for l in f.readlines():
-                yield l.strip()
+                email = l.strip()
+                if len(email) > 0:
+                    yield l.strip()
 
     @staticmethod
     def _get_unknown_email(emails):
@@ -86,12 +88,21 @@ class Command(BaseCommand):
                 except Member.DoesNotExist:
                     unknown_emails.append(email)
                 else:
-                    mls = MaillingListSubscription(
+                    mls_exists = MaillingListSubscription.objects.filter(
                         member=member,
                         maillinglist=ml,
-                    )
-                    mls.skip_sync = True
-                    mls.save()
+                    ).exists()
+
+                    # Not using get_or_create because we want to set skip_sync
+                    # before saving
+                    if not mls_exists:
+                        mls = MaillingListSubscription(
+                            member=member,
+                            maillinglist=ml,
+                        )
+                        mls.skip_sync = True
+                        mls.save()
+
 
         # Do it once… (db will be rollback if it fails)
         sys.stdout.write('Pousse la liste sur le serveur… ',)