Scan status fix

[TheTechromancer]

Fixes this bug:

watchdog-1  | [ERROR] Error ingesting event SCAN for applet Scans: cannot access local variable 'status_changed' where it is not associated with a value
watchdog-1  | [ERROR] Traceback (most recent call last):
watchdog-1  |   File "/app/bbot_server/watchdog/worker.py", line 86, in _event_listener
watchdog-1  |     _activities = await applet.handle_event(event, asset) or []
watchdog-1  |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
watchdog-1  |   File "/app/bbot_server/modules/scans/scans_api.py", line 318, in handle_event
watchdog-1  |     if status_changed:
watchdog-1  |        ^^^^^^^^^^^^^^
watchdog-1  | UnboundLocalError: cannot access local variable 'status_changed' where it is not associated with a value
watchdog-1  |

[aconite33]

Approved