ftp: removing uninitialized variable warning

output-json-ftp.c: In function ‘JsonFTPLogger’:
output-json-ftp.c:129:9: warning: ‘js_respcode_list’ may be used uninitialized in this function [-Wmaybe-uninitialized]
  129 |         json_object_set_new(cjs, "completion_code", js_respcode_list);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
output-json-ftp.c:74:13: note: ‘js_respcode_list’ was declared here
   74 |     json_t *js_respcode_list;
      |             ^~~~~~~~~~~~~~~~
output-json-ftp.c:128:9: warning: ‘js_resplist’ may be used uninitialized in this function [-Wmaybe-uninitialized]
  128 |         json_object_set_new(cjs, "reply", js_resplist);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
output-json-ftp.c:73:13: note: ‘js_resplist’ was declared here
   73 |     json_t *js_resplist;
      |             ^~~~~~~~~~~

src/output-json-ftp.c

@@ -70,8 +70,8 @@ static json_t *JsonFTPLogCommand(Flow *f, FTPTransaction *tx)
     }
 
     /* Preallocate array objects to simplify failure case */
-    json_t *js_resplist;
-    json_t *js_respcode_list;
+    json_t *js_resplist = NULL;
+    json_t *js_respcode_list = NULL;
     if (!TAILQ_EMPTY(&tx->response_list)) {
         js_resplist = json_array();
         js_respcode_list = json_array();