Fix for issue #186 (covers start as offline)

[rospogrigio]

This was due to wrong initialization values for _timer_start and _previous_state, should be fixed now.

[rospogrigio]

Dear @darth-aragoth and @makis , can you please check this PR and see if it fixes issue #186 ?
Thank you

[darth-aragoth]

Hello, it looks like this issue is fixed. Thank you.

[rospogrigio]

Merged #189 into master.

[userMak]

Hi
apparently there is still something wrong.
Today some of my covers where grayed out and I could not use them at all, even with the slider
The logs are

og Details (ERROR)
Logger: homeassistant
Source: components/tuya/__init__.py:146
First occurred: 7:44:52 AM (17 occurrences)
Last logged: 9:50:01 AM

Error doing job: Task exception was never retrieved
Traceback (most recent call last):
  File "/usr/src/homeassistant/homeassistant/components/tuya/__init__.py", line 153, in async_poll_devices_update
    device_list = await hass.async_add_executor_job(_get_updated_devices)
  File "/usr/local/lib/python3.8/concurrent/futures/thread.py", line 57, in run
    result = self.fn(*self.args, **self.kwargs)
  File "/usr/src/homeassistant/homeassistant/components/tuya/__init__.py", line 146, in _get_updated_devices
    tuya.poll_devices_update()
  File "/usr/local/lib/python3.8/site-packages/tuyaha/tuyaapi.py", line 166, in poll_devices_update
    return self.discover_devices()
  File "/usr/local/lib/python3.8/site-packages/tuyaha/tuyaapi.py", line 207, in discover_devices
    devices = self.discovery()
  File "/usr/local/lib/python3.8/site-packages/tuyaha/tuyaapi.py", line 188, in discovery
    response = self._request("Discovery", "discovery")
  File "/usr/local/lib/python3.8/site-packages/tuyaha/tuyaapi.py", line 267, in _request
    self._raise_frequently_invoke(
  File "/usr/local/lib/python3.8/site-packages/tuyaha/tuyaapi.py", line 292, in _raise_frequently_invoke
    raise TuyaFrequentlyInvokeException(message)
tuyaha.tuyaapi.TuyaFrequentlyInvokeException: Method [Discovery] fails 1 time(s) using poll interval 60.0 - error: you can discovery once in 600 seconds

and

Log Details (ERROR)
Logger: homeassistant.util.logging
Source: util/logging.py:108
First occurred: 7:39:52 AM (1 occurrences)
Last logged: 7:39:52 AM

Exception in _update_handler when dispatching 'localtuya_50758014840d8e91f036': ({},) Traceback (most recent call last): File "/config/custom_components/localtuya/common.py", line 245, in _update_handler self.status_updated() File "/config/custom_components/localtuya/cover.py", line 168, in status_updated if self._state.isupper(): AttributeError: 'NoneType' object has no attribute 'isupper'

[userMak]