fix(api): Fix memory leak and lost tx error

Use original TRYTES_81_3 as arugemnet of get_trytes() would
return null trytes response (all 9 response) which may result from
this transaction is lost in BD (snapshot or some reason else).
Using other exist transaction hash can solve this issue

Author: howjmay

accelerator/apis.c

@@ -116,6 +116,7 @@ status_t api_find_transactions_by_tag(
   ret = ta_find_transactions_res_serialize(json_result, res);
 
 done:
+  free(req_tag);
   ta_find_transactions_res_free(&res);
   return ret;
 }