[BUG] Show covering index runs into error when index is not present

[ps48]

What is the bug?
Show covering index runs into error when index is not present.
{"data":{"ok":true,"resp":{"status":"FAILED","error":"Fail to run query or write result"}}}

How can one reproduce the bug?
Steps to reproduce the behavior:

1. Make sure a covering index is not present in table ex.alb_logs.
2. Run SHOW INDEX ON myS3.default.alb_logs

What is the expected behavior?
This should return success with empty [] response.
Error/Failed state should only be sent when query execution runs into error.

[dai-chen]

It should be fixed in #81. Please verify latest artifact and let me know if still have issue. Thanks!

[dai-chen]

Feel free to reopen if any problem. Thanks!