Only force loading if delimiter is specified

When delimiter is passed into list_blobs, prefixes is not populated, loading is forced with next(blobs, None).

Do not attempt to iterate again over blobs if blobs.prefixes is empty and delimiter has been passed in.

This prevents the "iterator has already started" error message.

airflow/providers/google/cloud/hooks/gcs.py

@@ -821,11 +821,12 @@ def _list(
                     delimiter=delimiter,
                     versions=versions,
                 )
-                list(blobs)
+                if delimiter:
+                    next(blobs, None)
 
             if blobs.prefixes:
                 ids.extend(blobs.prefixes)
-            else:
+            elif not delimiter or (match_glob and delimiter == "/"):
                 ids.extend(blob.name for blob in blobs)
 
             page_token = blobs.next_page_token
@@ -933,11 +934,12 @@ def list_by_timespan(
                     delimiter=delimiter,
                     versions=versions,
                 )
-                list(blobs)
+                if delimiter:
+                    next(blobs, None)
 
             if blobs.prefixes:
                 ids.extend(blobs.prefixes)
-            else:
+            elif not delimiter or (match_glob and delimiter == "/"):
                 ids.extend(
                     blob.name
                     for blob in blobs

tests/providers/google/cloud/hooks/test_gcs.py

@@ -821,13 +821,18 @@ def test_provide_file_upload(self, mock_upload, mock_temp_file):
     @mock.patch(GCS_STRING.format("GCSHook.get_conn"))
     def test_list__delimiter(self, mock_service, prefix, result):
         mock_service.return_value.bucket.return_value.list_blobs.return_value.next_page_token = None
+        mock_service.return_value.bucket.return_value.list_blobs.return_value.prefixes = None
         with pytest.deprecated_call():
             self.gcs_hook.list(
                 bucket_name="test_bucket",
                 prefix=prefix,
                 delimiter=",",
             )
         assert mock_service.return_value.bucket.return_value.list_blobs.call_args_list == result
+        assert (
+            mock_service.return_value.bucket.return_value.list_blobs.return_value.__next__.call_count
+            == len(result)
+        )
 
     @mock.patch(GCS_STRING.format("GCSHook.get_conn"))
     @mock.patch("airflow.providers.google.cloud.hooks.gcs.functools")