Reconnecting client doesn't start with mid=1 again.

ChangeLog.txt

@@ -5,6 +5,8 @@ Broker:
 - Ensure websockets clients that previously connected with clean session set
   to false have their queued messages delivered immediately on reconnecting.
   Closes #476314.
+- Reconnecting client with clean session set to false doesn't start with mid=1
+  again.
 
 Client library:
 - Fix the case where a message received just before the keepalive timer

src/read_handle_server.c

@@ -456,6 +456,7 @@ int mqtt3_handle_connect(struct mosquitto_db *db, struct mosquitto *context)
 			found_context->subs = NULL;
 			context->sub_count = found_context->sub_count;
 			found_context->sub_count = 0;
+			context->last_mid = found_context->last_mid;
 
 			for(i=0; i<context->sub_count; i++){
 				if(context->subs[i]){