Handle bad UUIDs from third-party Chromecasts

[illixion]

Certain third-party Chromecast emulators like Reflector 4 broadcast bad UUIDs, which results in the entire pychromecast module failing to discover any devices when they're on the same network. This resolves the issue by ignoring said devices.

This also resolves issue #288.

For reference, this is the error message that pychromecast generates:

Traceback (most recent call last):
  File "/usr/local/lib/python3.8/threading.py", line 932, in _bootstrap_inner
    self.run()
  File "/usr/local/lib/python3.8/site-packages/zeroconf/__init__.py", line 1755, in run
    self._service_state_changed.fire(
  File "/usr/local/lib/python3.8/site-packages/zeroconf/__init__.py", line 1513, in fire
    h(**kwargs)
  File "/usr/local/lib/python3.8/site-packages/zeroconf/__init__.py", line 1611, in on_change
    listener.add_service(*args)
  File "/usr/local/lib/python3.8/site-packages/pychromecast/discovery.py", line 65, in add_service
    self._add_update_service(zconf, typ, name, self.add_callback)
  File "/usr/local/lib/python3.8/site-packages/pychromecast/discovery.py", line 107, in _add_update_service
    uuid = UUID(uuid)
  File "/usr/local/lib/python3.8/uuid.py", line 171, in __init__
    raise ValueError('badly formed hexadecimal UUID string')
ValueError: badly formed hexadecimal UUID string

[emontnemery]

Thanks!