Issue will be cloned back to itself if validator is not fulfilled

Summary of Bug

When cloning an issue, if there is a validator located in the workflow that is not fulfilled, JIRA will proceed with the cloning process anyway, and the clone process will end with the issue being linked to itself.

Steps to reproduce

1. Create a new workflow (or copy an existing one), without adding any new validators
2. Create a new workflow scheme
3. Assign the new workflow to the new scheme
4. Create a project, and use the new workflow scheme
5. Create an issue in the new project
6. Create a draft of the workflow, and insert a validator in the 'Create' transition such that a field is set as 'Required' during the transition (this is done using the JIRA Suite Utilities plugin)
7. Publish the draft
8. Access the existing issue, and try to clone it