Set editConfig to empty dict instead of None if there are no edit datasets

Author: manisandro

src/qwc2_viewer.py

@@ -1099,7 +1099,7 @@ def filter_edit_config(self, item, identity):
             item['editConfig'] = edit_config
         else:
             # no permitted datasets
-            item['editConfig'] = None
+            item['editConfig'] = {}
 
     def permitted_dataset(self, dataset, config, identity):
         """Return edit dataset filtered by permissions.