Reset error state when fetching todos from server.

Author: metamarcdw

src/reducers/todo_list.py

@@ -20,7 +20,8 @@ def todo_list_reducer(state=initial_state, action=None):
  if type_ == FETCH_ALL_TODOS_PENDING:
  return Object.assign({}, state, {
  "loading": True,
- "todos": []
+ "todos": [],
+ "error": None
  })
 
  elif type_ in (ADD_NEW_TODO_REJECTED, COMPLETE_TODO_REJECTED,