If something bad happens in spawnSync, stderr might be null. Therefore,
we have to check it before using it, so we won't mask the actual
exception.
Ref: https://github.com/nodejs/node/pull/9152
PR-URL: https://github.com/nodejs/node/pull/6877
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Robert Jefe Lindstädt <robert.lindstaedt@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>