Error when weather station is offline

[Cougar]

When weather station has been offline some time and there are no current measurements any more, this module should not try to use missing data

2024-07-14 01:06:25.005 ERROR (MainThread) [custom_components.wundergroundpws.coordinator] Check WUnderground API ('NO CURRENT RESULT',)
2024-07-14 01:06:25.056 ERROR (MainThread) [homeassistant] Error doing job: Task exception was never retrieved (None)
Traceback (most recent call last):
  File "/usr/src/homeassistant/homeassistant/helpers/update_coordinator.py", line 255, in _handle_refresh_interval
    await self._async_refresh(log_failures=True, scheduled=True)
  File "/usr/src/homeassistant/homeassistant/helpers/update_coordinator.py", line 411, in _async_refresh
    self.async_update_listeners()
  File "/usr/src/homeassistant/homeassistant/helpers/update_coordinator.py", line 165, in async_update_listeners
    update_callback()
  File "/usr/src/homeassistant/homeassistant/helpers/update_coordinator.py", line 491, in _handle_coordinator_update
    self.async_write_ha_state()
  File "/usr/src/homeassistant/homeassistant/helpers/entity.py", line 1007, in async_write_ha_state
    self._async_write_ha_state()
  File "/usr/src/homeassistant/homeassistant/helpers/entity.py", line 1133, in _async_write_ha_state
    state, attr, capabilities, shadowed_attr = self.__async_calculate_state()
                                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/src/homeassistant/homeassistant/helpers/entity.py", line 1068, in __async_calculate_state
    state = self._stringify_state(available)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/src/homeassistant/homeassistant/helpers/entity.py", line 1013, in _stringify_state
    if (state := self.state) is None:
                 ^^^^^^^^^^
  File "/usr/src/homeassistant/homeassistant/components/weather/__init__.py", line 871, in state
    return self.condition
           ^^^^^^^^^^^^^^
  File "/config/custom_components/wundergroundpws/weather.py", line 163, in condition
    day = self.coordinator.get_forecast(FIELD_FORECAST_ICONCODE)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/config/custom_components/wundergroundpws/coordinator.py", line 215, in get_forecast
    return self.data[FIELD_DAYPART][0][field][period]
           ~~~~~~~~~^^^^^^^^^^^^^^^
TypeError: 'NoneType' object is not subscriptable