After a message was reset in our caches cache via message editing or
adding/removing a reaction, we were sending corrupt data to the cache
because build_message_dict (and thus build_dict_from_raw_db_row) was
improperly being called before sewing in the reaction data.
As a result, we were sending raw database data in the reaction
dictionaries, rather than the reformatted version expected by the API.
Bug introduced in 2a4c62a326.
Fixing this correctly required moving the rendering_realm_id logic one
step higher in the call chain, which is a useful refactoring anyway
(since we're no longer passing a `Message` object down)
a53daa6f8c