Also fail ensure_dataset_on_disk if dataset is in new state

I believe this should cover https://sentry.galaxyproject.org/share/issue/0a9fcacfab584166910e14329e3a0e89/:
```
FileNotFoundError: [Errno 2] No such file or directory: ''
  File "galaxy/webapps/galaxy/services/datasets.py", line 637, in display
    rval, headers = dataset_instance.datatype.display_data(
  File "galaxy/datatypes/tabular.py", line 190, in display_data
    return self._serve_raw(dataset, to_ext, headers, **kwd)
  File "galaxy/datatypes/data.py", line 427, in _serve_raw
    headers["Content-Length"] = str(os.stat(dataset.get_file_name()).st_size)
InternalServerError: Could not get display data for dataset: [Errno 2] No such file or directory: ''
  File "starlette/_exception_handler.py", line 53, in wrapped_app
    await app(scope, receive, sender)
  File "starlette/routing.py", line 72, in app
    response = await func(request)
  File "fastapi/routing.py", line 278, in app
    raw_response = await run_endpoint_function(
  File "fastapi/routing.py", line 193, in run_endpoint_function
    return await run_in_threadpool(dependant.call, **values)
  File "starlette/concurrency.py", line 42, in run_in_threadpool
    return await anyio.to_thread.run_sync(func, *args)
  File "anyio/to_thread.py", line 56, in run_sync
    return await get_async_backend().run_sync_in_worker_thread(
  File "anyio/_backends/_asyncio.py", line 2144, in run_sync_in_worker_thread
    return await future
  File "anyio/_backends/_asyncio.py", line 851, in run
    result = context.run(func, *args)
  File "galaxy/webapps/galaxy/api/datasets.py", line 300, in display_history_content
    return self._display(request, trans, history_content_id, preview, filename, to_ext, raw, offset, ck_size)
  File "galaxy/webapps/galaxy/api/datasets.py", line 341, in _display
    display_data, headers = self.service.display(
  File "galaxy/webapps/galaxy/services/datasets.py", line 643, in display
    raise galaxy_exceptions.InternalServerError(f"Could not get display data for dataset: {util.unicodify(e)}")
```
It's a little hard to tell if this was really the reason here, but the
job went straight from new to paused. If the job state is new I don't
think we've even set the object store id yet.

lib/galaxy/managers/datasets.py

@@ -489,12 +489,16 @@ def serialize_dataset_association_roles(self, trans, dataset_assoc):
 
     def ensure_dataset_on_disk(self, trans, dataset):
         # Not a guarantee data is really present, but excludes a lot of expected cases
+        if not dataset.dataset:
+            raise exceptions.InternalServerError("Item has no associated dataset.")
         if dataset.purged or dataset.dataset.purged:
             raise exceptions.ItemDeletionException("The dataset you are attempting to view has been purged.")
         elif dataset.deleted and not (trans.user_is_admin or self.is_owner(dataset, trans.get_user())):
             raise exceptions.ItemDeletionException("The dataset you are attempting to view has been deleted.")
         elif dataset.state == Dataset.states.UPLOAD:
             raise exceptions.Conflict("Please wait until this dataset finishes uploading before attempting to view it.")
+        elif dataset.state == Dataset.states.NEW:
+            raise exceptions.Conflict("The dataset you are attempting to view is new and has no data.")
         elif dataset.state == Dataset.states.DISCARDED:
             raise exceptions.ItemDeletionException("The dataset you are attempting to view has been discarded.")
         elif dataset.state == Dataset.states.DEFERRED: