telepathyClient: ignore invalidated channels

There is a race if a channel is invalidated during its preparation: the
'invalidated' signal is already emitted so the Shell will never notice.
We fix this by simply checking if the channel is already invalidated when
receiving it from telepathy-glib.

In the approving case, we reject the full ChannelDispatchOperation as we only
support approving one channel at the time.

https://bugzilla.gnome.org/show_bug.cgi?id=677457

src/shell-tp-client.c

@@ -341,3 +341,9 @@ shell_decline_dispatch_op (TpAddDispatchOperationContext *context,
   tp_add_dispatch_operation_context_fail (context, error);
   g_error_free (error);
 }
+
+/* gjs doesn't cope with tp_proxy_get_invalidated() returning a GError */
+gboolean shell_is_channel_invalidated (TpChannel *channel)
+{
+  return tp_proxy_get_invalidated (channel) != NULL;
+}