Close any open message base after input timeout (5 minutes)

As Nelgin pointed out, the nntpservice can leave a message bases open while
a client is idle. Normally, an inactive client would be disconnected after 5
minutes of inactivity, so that wouldn't be much of an issue. However, if
authenticated as a user with the H-exemption, no auto-disconnection after
input timeout would happen. So let's close any open message base for good
measure.

The input/receive timeout probably should be configurable and lowered to
a smaller duration (one minute?). I'll leave that for another commit.

exec/nntpservice.js

@@ -199,6 +199,8 @@ while(client.socket.is_connected && !quit) {
 	cmdline = client.socket.recvline(1024 /*maxlen*/, 300 /*timeout*/);
 
 	if(cmdline==null) {
+		if(msgbase && msgbase.is_open)
+			msgbase.close();
 		if(client.socket.is_connected) {
 			if(user.security.exemptions&UFLAG_H)
 				continue;