domains: clear stack when no error handler

Clear domains stack __even if no domain error handler is set__ so that
code running in the process' uncaughtException handler, or any code that
may be executed when an error is thrown and not caught and that is not
the domain's error handler, doesn't run in the context of the domain
within which the error was thrown.

PR: #4659
PR-URL: https://github.com/nodejs/node/pull/4659


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>