TpSimplePasswordManager: don't keep a pointer to the challenge result
TpSimplePasswordManager: don't keep a pointer to the challenge result

The pointer goes stale when the result is consumed,
and it trips an assertion if the manager gets a new challenge.

Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib