Fix Fossil Type descriptors function

[bferguso]

If a Fossil Type is marked as a "Species", but it isn't attached to a Genus the bcfms/functions/bc_fossil_type_descriptors._get_parent_name function raises an excepation because the parent_value is None.

Should also add a function to validate that any fossil types marked as "Species" have a related Genus parent Fossil Type.

[bferguso]

This has led into an investigation about a potential other Arches Core issue where the relationships are not being deleted from the resource_x_resource table when a resource instance relationship is deleted from a resource.

This bug is confirmed by another user. Issue is here: archesproject/arches#11730