Fix to prevent connections to get terminated while still on going

[illera88]

I don't know how people could use it before this commit.

Connections get finished whenever the result from WaitForMultipleObjects errors to ERROR_IO_INCOMPLETE.

Testing:
Listen with:
ncat.exe -lvp 4444 --ssl

Connect with:
ncat.exe 127.0.0.1 4444 -e cmd.exe --ssl -v.

Run any command (i.e. dir) and it will close the connection.

Standard error is reported in the client and not in the server but I'll open a ticket to fix that.

Cheers

EDIT: stderr issue: #1373

[dmiller-nmap]

Thanks for the patch! This error is not mentioned in the "Return value" section of the documentation for GetOverlappedResult, but instead is up in the discussion of the bWarn parameter, so I had missed it. I modified your patch to use a switch statement, which I prefer for multiple comparisons of error values, but I credited you with the fix in the Changelog.