Fix AttributeError in update_mode when API returns None

[primmer10590]

Summary

When the Arlo API returns None from the active mode endpoint, update_mode() crashes with an AttributeError because it calls .get() on None. This causes a tight error loop that consumes excessive CPU.

Problem

AttributeError: 'NoneType' object has no attribute 'get'
  File "pyaarlo/location.py", line 158, in update_mode
    mode_id = data.get("properties", {}).get('mode')

This can happen when:

• The Arlo API is temporarily unavailable
• Network issues cause a failed request
• The API returns an unexpected response

Solution

Add a None check before accessing data, consistent with the existing pattern used in update_modes() just below this function.

Testing

• Tested with pyaarlo 0.8.0.17
• Verified the fix prevents the error loop when the API returns None
• Normal operation unaffected when API returns valid data