Pick a reasonable fallback wrap width when GetConsoleScreenBufferInfo() fails

[attie]

This PR resolves the initial problem raised in #9, and allows the output to be legible when GetConsoleScreenBufferInfo() fails.

This PR does not resolve the underlying issue.

Output with patch applied:

Attie@pongo MINGW64 /z/proj/scopehal/scopehal-apps/build
$ glscopeclient.exe scope:agilent:lan:scope.attie.co.uk:5025
GetConsoleScreenBufferInfo() failed (6);
Warning: glscopeclient works best with the OMP_WAI
T_POLICY environment variable set to PASSIVE
Warning: No Rx timeout: No error
Warning: No Tx timeout: No error
    Warning: Unknown trigger type "DEL"
    Warning: Unknown trigger type "DEL"
    Warning: Unknown trigger type "DEL"
    Warning: Unknown trigger type "DEL"
Warning: Unknown trigger type "DEL"
    Warning: Unknown trigger type "DEL"
[...]

Error 6 is ERROR_INVALID_HANDLE.