Stop some error messages being printed even when `--quiet` was used.

Thanks to Rob de Jonge.

Closes #1284.

ChangeLog.txt

@@ -43,8 +43,6 @@ Clients:
 - Fix mosquitto_pub not using the `-c` option. Closes #1273.
 - Fix MQTT v5 clients not being able to specify a password without a username.
   Closes #1274.
-
-Clients:
 - Fix `mosquitto_pub -l` not handling network failures. Closes #1152.
 - Fix double free on exit in mosquitto_pub. Closes #1280.
 
@@ -54,6 +52,7 @@ Documentation:
 
 Build:
 - CLIENT_LDFLAGS now uses LDFLAGS. Closes #1294.
+=======
 
 
 1.6.2 - 20190430

client/client_shared.c

@@ -1081,8 +1081,8 @@ int client_opts_set(struct mosquitto *mosq, struct mosq_config *cfg)
 	}
 	cfg->will_props = NULL;
 
-	if((cfg->username || cfg->password) && mosquitto_username_pw_set(mosq, cfg->username, cfg->password)){
-		err_printf(cfg, "Error: Problem setting username and/or password.\n");
+	if(cfg->username && mosquitto_username_pw_set(mosq, cfg->username, cfg->password)){
+		err_printf(cfg, "Error: Problem setting username and password.\n");
 		mosquitto_lib_cleanup();
 		return 1;
 	}