libwebsockets

ss: use system trust store if none given in policy

For general OpenSSL case, we leave connection validity to system trust
store bundle to decide; even for mbedtls it may have been passed a
bundle externally and we don't want to have to list the x.509 stack
explicitly for a server we don't have any control over.

Instead of erroring out, allow the case no trust store is specified,
just use vhost[0] and let the system trust store decide if it likes
the server's cert or not.


No ABI change.