fix load_stac from unsigned job results URL #402

Traceback (most recent call last):
  File "/opt/venv/lib64/python3.8/site-packages/flask/app.py", line 1516, in full_dispatch_request
    rv = self.dispatch_request()
  File "/opt/venv/lib64/python3.8/site-packages/flask/app.py", line 1502, in dispatch_request
    return self.ensure_sync(self.view_functions[rule.endpoint])(**req.view_args)
  File "/opt/venv/lib64/python3.8/site-packages/openeo_driver/users/auth.py", line 88, in decorated
    return f(*args, **kwargs)
  File "/opt/venv/lib64/python3.8/site-packages/openeo_driver/views.py", line 619, in result
    result = backend_implementation.processing.evaluate(process_graph=process_graph, env=env)
  File "/opt/venv/lib64/python3.8/site-packages/openeo_driver/ProcessGraphDeserializer.py", line 277, in evaluate
    return evaluate(process_graph=process_graph, env=env)
  File "/opt/venv/lib64/python3.8/site-packages/openeo_driver/ProcessGraphDeserializer.py", line 348, in evaluate
    result = convert_node(result_node, env=env)
  File "/opt/venv/lib64/python3.8/site-packages/openeo_driver/ProcessGraphDeserializer.py", line 368, in convert_node
    process_result = apply_process(process_id=process_id, args=processGraph.get('arguments', {}),
  File "/opt/venv/lib64/python3.8/site-packages/openeo_driver/ProcessGraphDeserializer.py", line 1480, in apply_process
    args = {name: convert_node(expr, env=env) for (name, expr) in sorted(args.items())}
  File "/opt/venv/lib64/python3.8/site-packages/openeo_driver/ProcessGraphDeserializer.py", line 1480, in <dictcomp>
    args = {name: convert_node(expr, env=env) for (name, expr) in sorted(args.items())}
  File "/opt/venv/lib64/python3.8/site-packages/openeo_driver/ProcessGraphDeserializer.py", line 380, in convert_node
    return convert_node(processGraph['node'], env=env)
  File "/opt/venv/lib64/python3.8/site-packages/openeo_driver/ProcessGraphDeserializer.py", line 368, in convert_node
    process_result = apply_process(process_id=process_id, args=processGraph.get('arguments', {}),
  File "/opt/venv/lib64/python3.8/site-packages/openeo_driver/ProcessGraphDeserializer.py", line 1512, in apply_process
    return process_function(args=ProcessArgs(args, process_id=process_id), env=env)
  File "/opt/venv/lib64/python3.8/site-packages/openeo_driver/ProcessGraphDeserializer.py", line 2088, in load_stac
    return env.backend_implementation.load_stac(url=url, load_params=load_params, env=env)
  File "/opt/venv/lib64/python3.8/site-packages/openeogeotrellis/backend.py", line 1031, in load_stac
    itm.properties.get("datetime") or itm.properties["start_datetime"],
KeyError: 'start_datetime'

openeogeotrellis/backend.py

@@ -926,7 +926,7 @@ def operator_value(criterion: Dict[str, object]) -> (str, object):
             for asset_id, asset in self.batch_jobs.get_result_assets(job_id=job_id, user_id=user.user_id).items():
                 pystac_item = pystac.Item(id=asset_id, geometry=asset["geometry"], bbox=asset["bbox"],
                                           datetime=rfc3339.parse_datetime(asset["datetime"], with_timezone=True),
-                                          properties={})
+                                          properties={"datetime": asset["datetime"]})
 
                 if intersects_spatiotemporally(pystac_item) and "data" in asset.get("roles", []):
                     eo_bands = [{"name": b.name} for b in asset["bands"]]