Fix PyTorch fatbinary dumping

[yuhc]

Description

The previous dump spec failed to dump fatbinaries with no kernel or no useful kernel. This diff handles this corner case.

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Document update (this change is mainly a documentation update)

Checklist:

• [x] My code passes format and lint checks.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] I have commented my code, particularly in hard-to-understand areas.
• [ ] My changes generate no new warnings.
• [ ] I have tested my code with a reasonable workload.
• [ ] My code may break some other features.