Fix reconnect+will delay interval issue causing missing messages.

Fix clients not receiving messages after a previous client with the same   client ID and positive will delay interval quit.
Closes #1752. Thanks to Jiří Zuzaňák.

ChangeLog.txt

@@ -24,6 +24,8 @@ Broker:
 - Don't try to start DLT logging if DLT unavailable, to avoid a long delay
   when shutting down the broker. Closes #1735.
 - Fix potential memory leaks. Closes #1773. Closes #1774.
+- Fix clients not receiving messages after a previous client with the same
+  client ID and positive will delay interval quit. Closes #1752.
 
 Client library:
 - Improved documentation around connect callback return codes. Close #1730.

lib/will_mosq.c

@@ -120,6 +120,7 @@ int will__clear(struct mosquitto *mosq)
 
 	mosquitto__free(mosq->will);
 	mosq->will = NULL;
+	mosq->will_delay_interval = 0;
 
 	return MOSQ_ERR_SUCCESS;
 }