Fix potential duplicate Will messages being sent.

This could have occurred when a will delay interval had been set.

ChangeLog.txt

@@ -1,3 +1,8 @@
+Broker:
+- Fix potential duplicate Will messages being sent when a will delay interval
+  has been set.
+
+
 2.0.5 - 2021-01-11
 ==================
 

src/will_delay.c

@@ -40,6 +40,10 @@ int will_delay__add(struct mosquitto *context)
 {
 	struct will_delay_list *item;
 
+	if(context->will_delay_entry){
+		return MOSQ_ERR_SUCCESS;
+	}
+
 	item = mosquitto__calloc(1, sizeof(struct will_delay_list));
 	if(!item) return MOSQ_ERR_NOMEM;