Bugfix in invalidation of UI. Fixes an issue when the application switches to another event loop.

Author: jonathanslenders

prompt_toolkit/application/application.py

@@ -736,6 +736,13 @@ def flush_input() -> None:
  async def _run_async2() -> _AppResult:
  self._is_running = True
 
+ # Make sure to set `_invalidated` to `False` to begin with,
+ # otherwise we're not going to paint anything. This can happen if
+ # this application had run before on a different event loop, and a
+ # paint was scheduled using `call_soon_threadsafe` with
+ # `max_postpone_time`.
+ self._invalidated = False
+
  loop = get_event_loop()
  if set_exception_handler:
  previous_exc_handler = loop.get_exception_handler()