Error in AP scanning causes hang

[jantman]

Bug Report

Version

Current pre-release @ 6a35b74

Installation Method

Docker image jantman/python-wifi-survey-heatmap:6a35b74

Supporting Software Versions

N/A - Docker

Actual Output

While running a survey/scan, the UI gets to 80% on the first point (status bar says "Scanning all access points within reach") and then just... hangs there. Looking at the console output, I see the following error:

2022-01-29 13:12:57,737 [DEBUG collector.py:102 - wifi_survey_heatmap.collector.scan_all_access_points() ] Scanning...
Traceback (most recent call last):
  File "/app/wifi_survey_heatmap/ui.py", line 295, in onLeftUp
    self._do_measurement(pos)
  File "/app/wifi_survey_heatmap/ui.py", line 411, in _do_measurement
    res['scan_results'] = self.collector.scan_all_access_points()
  File "/app/wifi_survey_heatmap/collector.py", line 103, in scan_all_access_points
    res = self.scanner.scan_all_access_points()
  File "/app/wifi_survey_heatmap/libnl.py", line 299, in scan_all_access_points
    pack = struct.pack('16sI', self.interface_name.encode('ascii'), 0)
AttributeError: 'NoneType' object has no attribute 'encode'

Expected Output

No error.