Set group.pubid before returning open groups

`GroupCreateService.create_private_group()` and
`GroupCreateService.create_restricted_group()` both return
`models.Group` objects whose `pubid` attribute has already been
generated, but `GroupCreateService.create_open_group()` returns groups
with `pubid=None` because the value for `pubid` won't be generated until
the group is flushed to the DB.

This is a likely source of errors (for example the API returning
`id: null` in the JSON response when creating an open group) so fix
`GroupCreateService` to generate `pubid`'s also for open groups before
returning the group to the caller.

h/services/group_create.py

@@ -128,12 +128,13 @@ def _create(  # pylint: disable=too-many-arguments
         )
         self.db.add(group)
 
+        # Flush the DB to generate `group.pubid` before passing `group` to
+        # self.publish() or `return group`.
+        self.db.flush()
+
         if add_creator_as_member:
             group.members.append(group.creator)
 
-            # Flush the DB to generate group.pubid before publish()ing it.
-            self.db.flush()
-
             self.publish("group-join", group.pubid, group.creator.userid)
 
         return group

tests/unit/h/services/group_create_test.py

@@ -14,6 +14,7 @@ def test_it_returns_group_model(self, creator, svc):
         group = svc.create_private_group("Anteater fans", creator.userid)
 
         assert isinstance(group, Group)
+        assert group.pubid
 
     def test_it_sets_group_name(self, creator, svc):
         group = svc.create_private_group("Anteater fans", creator.userid)
@@ -118,6 +119,7 @@ def test_it_returns_group_model(self, creator, svc, origins):
         group = svc.create_open_group("Anteater fans", creator.userid, scopes=origins)
 
         assert isinstance(group, Group)
+        assert group.pubid
 
     @pytest.mark.parametrize(
         "group_attr,expected_value",
@@ -258,6 +260,7 @@ def test_it_returns_group_model(self, creator, svc, origins):
         )
 
         assert isinstance(group, Group)
+        assert group.pubid
 
     @pytest.mark.parametrize(
         "group_attr,expected_value",