some pulls/issues are not migrated on resume

[ViliusS]

In some cases pull requests or issues are skipped. Such cases include:

• If multiple GitLab merge requests have the same words (like Jira ticket numbers) in title, and you stop and resume migration second time.
• If GitLab merge requests have exactly the same title, and you stop and resume migration second time.
• If somebody already started to work on GitHub repository and created a merge request or an issue with the same or similar name, and you try to migrate GitLab merge requests at later time.

Basically it skips at this line, however I'm struggling to think of a good way to solve this.