fix: server sending "227 Logout." response

Sometimes if the data connection for passive mode was interrupted, the
server would send "227 Logout." response. However this response was
being blocked by Linux's netfiter connection tracking FTP helper.

src/ftp_parser.c

@@ -263,7 +263,7 @@ void parser(void)
             die(421, LOG_INFO, MSG_TIMEOUT_PARSER);
 #endif
         case -2:
-            return;
+            die(425, LOG_INFO, MSG_LOGOUT);
         }
 #ifdef DEBUG
         if (debug != 0) {