inspector: fix crash on exception

Fixes: https://github.com/nodejs/node/issues/13438
PR-URL: https://github.com/nodejs/node/pull/13455


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>