fix: handle missing hci devices when enumerating adapters

[bdraco]

Traceback (most recent call last):
  File "/usr/src/homeassistant/homeassistant/setup.py", line 404, in _async_setup_component
    result = await task
             ^^^^^^^^^^
  File "/usr/src/homeassistant/homeassistant/components/bluetooth/__init__.py", line 235, in async_setup
    await manager.async_setup()
  File "/usr/src/homeassistant/homeassistant/components/bluetooth/manager.py", line 133, in async_setup
    await super().async_setup()
  File "src/habluetooth/manager.py", line 262, in async_setup
  File "src/habluetooth/manager.py", line 212, in _async_refresh_adapters
  File "/usr/local/lib/python3.12/site-packages/bluetooth_adapters/systems/linux.py", line 123, in adapters
    product = uart_device.product
              ^^^^^^^^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'product'