Let `convert_to_esbulk.py` accept empty DFs
In case of an empty DF, return with code 2
Bug: T358472
How to register an account on GitLab. To prevent spam, new accounts are locked until approved by an admin or the approver bot. You can also file an unlock request to expedite access.
Support: mw:GitLab, how to host a project on GitLab, #wikimedia-gitlab on libera.chat, #GitLab on Phabricator.
In case of an empty DF, return with code 2
Bug: T358472