Prevent blocked ports from being used

[notcreative]

New user - be gentle: I'm not sure if this falls into a bug - or a feature request.
runApp() chooses a port blacklisted by internet browser: port 6697 and returns ERR_UNSAFE_PORT error. The error does not exist if I choose another open/unblocked port.

I recommend maintaining list of blacklisted ports to avoid during the runApp() call.

Link to port blocking info:
[https://bugs.chromium.org/p/chromium/issues/detail?id=676951]

[wch]

Thanks for the report!