Replace silent error swallowing (err == nil) with proper error distinction
for bucket policy reads. Now properly checks ErrAttributeNotFound and
propagates other errors as internal server errors.
Fixed 5 locations:
- handleCreateNamespace (policy fetch)
- handleDeleteNamespace (policy fetch)
- handleListNamespaces (policy fetch)
- handleGetNamespace (policy fetch)
- handleGetTableBucket (policy fetch)
This prevents masking of filer issues when policies cannot be read due
to I/O errors or other transient failures.
2c45b69775