Fix: Check for value of remote post id to verify push result

[dinhtungdu]

Description of the Change

We're checking for the existence of post_id key, not the value of it. There is a case where post_id equals 0, and we still assume that the push is successful.
See #488 (comment)

For some reasons, I can't update #492, this PR is made to replace it.

Verification Process

See #488 (comment).

Checklist:

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests passed.

Applicable Issues

Fixes #488 and closes #492.

Changelog Entry

[dinhtungdu]

Note that we still need #570 to be merged for passing the tests.