Check quarantined blob existence in main repository before size limit

What does this MR do and why?

Following up on !127919 (comment 1504970116)

Check quarantined blob existence in main repository before size limit

When checking the quarantine directory for new blobs it is sometimes possible for there to be blobs that are already present in the main repository.

Mitigate this by checking for existence of blobs in the main repository

Contributes to: #393535 (closed)

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #393535 (closed)