Exception in routing_context::start()

[Tectu]

Inside of malloy::server::routing_context::start(), we make a call to boost::asio::ip::make_address().
If the supplied string cannot be converted to an IP address, an exception is thrown.

There is an overload of make_address() which accepts an error_code output. We should use that one.
However, the problem is that we might not "fail safely" from this function as we still have to return a session.

This was discovered by passing "localhost" into make_address().