Container Registry image tags can be invalid which prevents deletion

Summary

Investigating issues with image tag deletion and there are tags in the system which do not have a digest. Without the digest a deletion cannot be carried out

Steps to reproduce

Unsure of steps to reproduce but we have projects that on GitLab.com with invalid tags

Example Project

https://gitlab.com/vais/tts-worker-hts/container_registry

What is the current bug behavior?

Image tag deletion does nothing

What is the expected correct behavior?

Image tag deletion should remove the tag

Relevant logs and/or screenshots

(Paste any relevant logs - please use code blocks (```) to format console output, logs, and code as it's very hard to read otherwise.)

Output of checks

GitLab.com v10.1.3

Possible fixes

(If you can, link to the line of code that might be responsible for the problem)