text: Title: [BUG] `save_changes()` doesn't throw an error when document doesn't exists
  Body: **Describe the bug**
  In 1.11.9 state was changed and always defaults being not None, instead it got a dict with the default values. This causes `check_if_state_saved` to never throw an error.
  
  `save_changes` on a new created document that isn't saved in the database silently does nothing.
  
  **To Reproduce**
  ```python
  user_data = UserEntry(...)
  user_data.x = ...
  await user_data.save_changes()
  ```
  
  **Expected behavior**
  `StateNotSaved("No state was saved")`
  **Additional context**
  https://github.com/roman-right/beanie/compare/1.11.8...1.11.9
  https://canary.discord.com/channels/822196934973456394/822196935435747332/1042243293662158970
  