Deleting of a graph fails if one of the associated instances references a concept in the primary display that has been deleted

[apeters]

if a user deletes a concept that is referenced in a primary display for a resource, then deleting that resource throws an error (and so does deleting the associated graph).

this is caused by not appropriately handling for when the 'get' method throws a DoesNotExist errr on this line:
https://github.com/archesproject/arches/blob/5.0.0/arches/app/datatypes/concept_types.py#L32

see this thread for a stack trace:
https://groups.google.com/forum/?utm_medium=email&utm_source=footer#!msg/archesproject/XX26MV55LUo/d2Cv1OTZAgAJ

[whatisgalen]

Unable to reproduce: Unable to delete a concept in RMD manager that is being used in a resource instance's primary descriptor. Error:
Unable to Delete
This concept or one of it's subconcepts is already in use by an existing resource.

[apeters]

It looks like the user, instead of deleting just the concept, was able to delete the entire thesauri and collection. This is what ultimately caused the issue. Can you confirm this?

[whatisgalen]

Ok yes I can confirm that if you delete the collection and thesauri that reproduces the issue.

[apeters]

fixed in #6377