_g_dbus_worker_new: hold a ref until we have done the initial read
_g_dbus_worker_new: hold a ref until we have done the initial read

Otherwise, we could use-after-free the GDBusWorker, if its last-unref
is immediately after _g_dbus_worker_new returns (before the worker thread
does its initial read).

Bug: https://bugzilla.gnome.org/show_bug.cgi?id=651268
Bug-NB: NB#271520
Signed-off-by: Simon McVittie <2b470b34502dbf3ba4bcc04ea7e64f4e0e104f33@collabora.co.uk>
Signed-off-by: David Zeuthen <16a4bae6a7afea1fdd75baca6404fe68f285db96@redhat.com>

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