I think this is the fix but please verify.  I added type of 'R' to your where statement in the select under DB LEVEL PERMISSIONS.

WHERE [perm].[major_id] = 0

AND [usr].[principal_id] >...

Can you add code to output Roles that are assigned permissions at the Database level?  It looks like I'm only seeing users in the output.  example:  I create a role...