Avoid sending blob candidate for deletion event for empty_picture.png

In the source/blob stream we can see many times that the blob empty_picture is marked as candidate for blob deletion.
We should avoid blob/gc computation to process such event, because this blob is an internal one it's just a waste of time.
We want to avoid publishing this event for this internal blob.

Reproduction

When creating a Picture document without a blob and then editing this Picture document to add a picture file, a Thumbnail and picture views generation occurs.

Fields such as views/*/content are edited and we produce a blobCandidateForDeletion blob domain event that will eventually write to the source/blob stream a record to check if the old blob value empty_picture.png is orphaned.