On Windows, closing FFT window crashes Mavexplorer

Hi everyone.

Behaviour: I load a log, run FFT on it, close one of the windows, Mavexplorer crashes. Running from the command line, there is error output:
`PS C:\Program Files (x86)\MAVProxy> Traceback (most recent call last):
File "MAVProxy\modules\lib\wxconsole_ui.py", line 90, in on_idle
File "multiprocessing\connection.py", line 206, in send
File "multiprocessing\connection.py", line 280, in _send_bytes
BrokenPipeError: [WinError 232] Die Pipe wird gerade geschlossen` [Pipe is being closed]

I am on Windows 10, installed via the prebuilt installer.

Reproduce the crash on Windows 10 by loading a log, running FFT, and closing one FFT window. Start in MAVProxy/modules/lib/wxconsole_ui.py at line 90 and inspect the reported multiprocessing pipe error. Done means closing the FFT window no longer crashes Mavexplorer or produces the BrokenPipeError.

Written by the indexing model from the issue text.