bug: Crash when loading calibration data.

[sp9rqa]

Bug Report

**NanoVNA-Saver version: 0.5.5

0.5.5

Current behavior:
The application closes.

Expected behavior:
Well rather it should work ;-)

Steps to reproduce:

Attempting to load any calibration file.
Related code:

Traceback (most recent call last):
File "NanoVNASaver/Windows/CalibrationSettings.py", line 142, in
File "NanoVNASaver/Windows/CalibrationSettings.py", line 604, in loadCalibration
File "NanoVNASaver/Calibration.py", line 436, in load
File "NanoVNASaver/Calibration.py", line 201, in from_str
File "NanoVNASaver/Calibration.py", line 170, in _append_match
TypeError: float() argument must be a string or a real number, not 'NoneType'

Other information:

System Debian Testing
Python 3.11.2