Include connection errors in exception handling

ref-test/app/tools/forms.py

@@ -50,7 +50,7 @@ def get_time_options():
 def get_dataset_choices():
     from ..models import Dataset
     try: datasets = Dataset.query.all()
-    except SQLAlchemyError as exception:
+    except (SQLAlchemyError, ConnectionError) as exception:
         write('system.log', f'Database error when fetching dataset lists: {exception}')
         return []
     dataset_choices = []