fd.o #30949: tp_message_mixin_get_dbus_property: fix DeliveryReportingSupport
fd.o #30949: tp_message_mixin_get_dbus_property: fix DeliveryReportingSupport

Previously, we'd always say it was 0 due to a typo in the method.

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