Fix error C2065: 'errorMsg': undeclared identifier

[Cheney-W]

I am a maintainer of vcpkg, and when I updated ixwebsocket to version 11.4.4, I encountered the following errors:

\ixwebsocket\IXSocketMbedTLS.cpp(61): error C2065: 'errorMsg': undeclared identifier
\ixwebsocket\IXSocketMbedTLS.cpp(62): error C2065: 'errorMsg': undeclared identifier
\ixwebsocket\IXSocketMbedTLS.cpp(88): error C2065: 'errorMsg': undeclared identifier

Above errors occurred because errorMsg was commented out in PR #399, I don't know why it was commented out.

To fix this issue, I uncomment the codes.

[bsergean]

Thanks for the fix. That other PR that commented it out probably did that to remove a compiler warning on non-windows platforms.