parser: Always use a valid GError internally
parser: Always use a valid GError internally

Do not just pass the GError through from the public-facing arguments: we
may want to perform error checking internally at any later date.

Distrotech/json-glib,ebassi/json-glib,Distrotech/json-glib,frida/json-glib,frida/json-glib,Distrotech/json-glib,ebassi/json-glib,GNOME/json-glib,ebassi/json-glib,GNOME/json-glib