src: handle thrown errors in CopyProperties()

This commit prevents thrown JavaScript exceptions from crashing
the process in node_contextify's CopyProperties() function.

Fixes: https://github.com/nodejs/node/issues/8537
PR-URL: https://github.com/nodejs/node/pull/8649


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ilkka Myller <ilkka.myller@nodefield.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>