Fix critical assertion when secret_password_lookup_xx() returns null.
Fix critical assertion when secret_password_lookup_xx() returns null.

Distrotech/libsecret,Distrotech/libsecret,GNOME/libsecret,GNOME/libsecret,Distrotech/libsecret,stefwalter/libsecret,Distrotech/libsecret,stefwalter/libsecret,Distrotech/libsecret,stefwalter/libsecret,stefwalter/libsecret,GNOME/libsecret,GNOME/libsecret,stefwalter/libsecret