Catch DoesNotExist preventing startup

Fixes failing startup because of python error:

```
Traceback (most recent call last):
  File "/opt/netbox/netbox/./manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/opt/netbox/venv/lib/python3.10/site-packages/django/core/management/__init__.py", line 446, in execute_from_command_line
    utility.execute()
  File "/opt/netbox/venv/lib/python3.10/site-packages/django/core/management/__init__.py", line 440, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/opt/netbox/venv/lib/python3.10/site-packages/django/core/management/base.py", line 402, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/opt/netbox/venv/lib/python3.10/site-packages/django/core/management/base.py", line 448, in execute
    output = self.handle(*args, **options)
  File "/opt/netbox/venv/lib/python3.10/site-packages/django/core/management/commands/shell.py", line 127, in handle
    exec(sys.stdin.read(), globals())
  File "<string>", line 2, in <module>
  File "/opt/netbox/venv/lib/python3.10/site-packages/django/db/models/manager.py", line 85, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/opt/netbox/venv/lib/python3.10/site-packages/django/db/models/query.py", line 650, in get
    raise self.model.DoesNotExist(
users.models.Token.DoesNotExist: Token matching query does not exist.
```

docker/docker-entrypoint.sh

@@ -84,9 +84,12 @@ fi
 
 ./manage.py shell --interface python <<END
 from users.models import Token
-old_default_token = Token.objects.get(key="0123456789abcdef0123456789abcdef01234567")
-if old_default_token:
-    print("⚠️ Warning: You have the old default admin token in your database. This token is widely known; please remove it.")
+try:
+    old_default_token = Token.objects.get(key="0123456789abcdef0123456789abcdef01234567")
+    if old_default_token:
+        print("⚠️ Warning: You have the old default admin token in your database. This token is widely known; please remove it.")
+except Token.DoesNotExist:
+    pass
 END
 
 echo "✅ Initialisation is done."