Bulk Export requests on non-existent Patient or Group resources generate 500 errors instead of 404 errors

[michaelabuckley]

Describe the bug

Invoking /Group/abc/$export or /Patient/$export?patient=abc when the resources Group/abc and Patient/abc do not exists will start a batch job that fails with a 500 error. We would expect the request to fail with a 404.

Expected behavior

Throw "not found 404" when the target of a bulk export does not exist.

[michaelabuckley]

Fixed in #4890