updated test_validate_site_model to consider a degenerate case
updated test_validate_site_model to consider a degenerate case


Former-commit-id: 30f9fa1768ba20d05bce69783b4c22ac09708753 [formerly 80d0250ef397c39403feb3bb4aee545c664840d1]
Former-commit-id: d066a5da2428dbffbca395b7d94a349b44015595
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine