Fix overwriting verification key upon sending confirmation mail

ivatar/ivataraccount/models.py

@@ -359,6 +359,7 @@ class UnconfirmedEmail(BaseAccountModel):
 
     def save(self, force_insert=False, force_update=False, using=None,
              update_fields=None):
+        if not self.verification_key:
             hash_object = hashlib.new('sha256')
             hash_object.update(
                 urandom(1024) + self.user.username.encode('utf-8')  # pylint: disable=no-member