file monitor: Fix invalid read
file monitor: Fix invalid read

Commit 7373acf changed file monitor construction to be really
synchronous. Unfortunately there is missing g_object_ref for d-bus
connection and the connection is unrefed after use. Subsequent read
of the unrefed connection cause crash with following critical:

(firefox:29844): GLib-GIO-CRITICAL **: g_dbus_connection_is_closed:
assertion 'G_IS_DBUS_CONNECTION (connection)' failed

Do not store the connection, because it isn't neccesary with the
synchronous construction.

https://bugzilla.gnome.org/show_bug.cgi?id=756153

gicmo/gvfs,gicmo/gvfs,gicmo/gvfs,gicmo/gvfs