Nonexisting message tables are still accessed, causing errors

[bbangert]

May 05 16:52:04 ip-172-31-39-23 python[11560]: File "/data/autopush/app/autopush/router/webpush.py", line 74, in preflight_check
May 05 16:52:04 ip-172-31-39-23 python[11560]: self.ap_settings.message_tables[month_table].all_channels,
May 05 16:52:04 ip-172-31-39-23 python[11560]: exceptions.KeyError: u'prod.autopush.message_2016_3' 

It appears no handling is done to ensure the user has a new enough month when delivering messages. Since message tables 'too old' should be considered users who will be invalidated on a new connect, this issue should be handled as a 410 since the endpoint will never be valid again.