n-api: add missed nullptr check in napi_has_own_property

PR-URL: https://github.com/nodejs/node/pull/30626


Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Chengzhong Wu <legendecas@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>