[0.6.0-rc2 QA] Client crashes on login if user was logged out due to deletion

[eloquence]

Environment: Qubes 4.0.4, staging environment, RC2 0.6.0 package, 2.1.0 prod server

STR

1. Create a user with username = "deleteme"
2. Log into the client as the user
3. Send a reply as the user (not sure if necessary)
4. Disconnect the workstation from the network
5. Delete the user via the Journalist Interface on another computer
6. Reconnect the workstation to the network
7. Wait until you get bounced to the login screen with a session expiry error
8. Log back in as a different user

Expected behavior

User is logged in

Actual behavior

Client crashes. Logs say:

2022-02-02 16:40:57,179 - securedrop_client.logic:534(on_authenticate_success) INFO: erik successfully logged in
2022-02-02 16:40:57,193 - root:63(excepthook) ERROR: Unrecoverable error
Traceback (most recent call last):
  File "/opt/venvs/securedrop-client/lib/python3.7/site-packages/securedrop_client/gui/widgets.py", line 2037, in _on_update_authenticated_user
    if user.uuid == self.sender.uuid:
  File "/opt/venvs/securedrop-client/lib/python3.7/site-packages/sqlalchemy/orm/attributes.py", line 276, in __get__
    return self.impl.get(instance_state(instance), dict_)
  File "/opt/venvs/securedrop-client/lib/python3.7/site-packages/sqlalchemy/orm/attributes.py", line 677, in get
    value = state._load_expired(state, passive)
  File "/opt/venvs/securedrop-client/lib/python3.7/site-packages/sqlalchemy/orm/state.py", line 660, in _load_expired
    self.manager.deferred_scalar_loader(self, toload)
  File "/opt/venvs/securedrop-client/lib/python3.7/site-packages/sqlalchemy/orm/loading.py", line 985, in load_scalar_attributes
    raise orm_exc.ObjectDeletedError(state)
sqlalchemy.orm.exc.ObjectDeletedError: Instance '<User at 0x70ff1a06bc50>' has been deleted, or its row is otherwise not present.
(END)

This error is ephemeral: after restarting the client, the error goes away.

[sssoleileraaa]

I was able to repro just now 🎉