Don't disconnect clients that are already disconnected.

This prevents the session expiry being extended on SIGHUP.

Closes #1521. Thanks to Christoph Krey.

ChangeLog.txt

@@ -5,6 +5,11 @@ Broker:
   correctly. Creating a new user with `-b` worked without problem.
   Closes #1664.
 - Fix memory leak when connecting clients rejected.
+- Don't disconnect clients that are already disconnected. This prevents the
+  session expiry being extended on SIGHUP. Closes #1521.
+ 
+ 1.6.8 - 20191128
+ ================
 
 Client library:
 - Don't treat an unexpected PUBACK, PUBREL, or PUBCOMP as a fatal error.

src/context.c

@@ -226,6 +226,10 @@ void context__send_will(struct mosquitto_db *db, struct mosquitto *ctxt)
 
 void context__disconnect(struct mosquitto_db *db, struct mosquitto *context)
 {
+	if(mosquitto__get_state(context) == mosq_cs_disconnected){
+		return;
+	}
+
 	net__socket_close(db, context);
 
 	context__send_will(db, context);