Fixed issue where metadata would come with garbage

[Tjoms99]

Investigated the PR/issue discussed here #49.

Turns out not properly exiting a program running the PPK2 influences the next PPK2 session. Setting up the metadata the first time will throw an exception due to the garbage data (from the previous session) that comes a long with it. Physically turning the PPK2 on and off using the switch resolves this issue, but that’s inconvenient to do every time; So I’ve added a software fix here :)

To reproduce the issue and showcase the fix

1. Connect the PPK2 via USB

2. Open a terminal and run the example

python3 examples/example_measure_mw.py

3. Terminate the program (2x)

ctrl + c

4. Run the example again and you'll probably see this in the terminal

Attempt 1/2 - Failed to get valid PPK2 metadata: Could not retrieve valid metadata from the device.
Attempt 2/2 - Got metadata from PPK2
Initialized Power Profiler

This is where the UnicodeDecodeError would previously be triggered

[RmThrt]

Thanks for the fix, it helped to figure out the way my test work! Good fix for me :)