Check for empty omics_processings list

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: naglepuff

nmdc_server/crud.py

@@ -439,6 +439,11 @@ def construct_zip_file_path(data_object: models.DataObject) -> str:
     #   - We probably want to reference the workflow activity but that
     #     involves a complicated query... need a way to join that information
     #     in the original query (possibly in the sqlalchemy relationship)
+    if not data_object.omics_processings:
+        raise HTTPException(
+            status_code=status.HTTP_400_BAD_REQUEST,
+            detail="Data object has no associated omics processings."
+        )
     omics_processing = data_object.omics_processings[0]
     biosamples = cast(Optional[list[models.Biosample]], omics_processing.biosample_inputs)