tp_account_dup_storage_identifier_variant: deal with storage_identifier being NULL
tp_account_dup_storage_identifier_variant: deal with storage_identifier being NULL

https://bugs.freedesktop.org/show_bug.cgi?id=53201

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