rtpbin: unitialized value

This is a regression since b5e414cd in gst_rtp_bin_handle_message()

  guint64 last_out;

  /* Not called, therefore last_out not initialize */
  if (g_signal_lookup ("set-active", G_OBJECT_TYPE (element)) != 0) {
    g_signal_emit_by_name (element, "set-active", active, offset,
           &last_out);
  }

  if (!active) {
    g_object_get (element, "percent", &stream->percent, NULL);

    /* Using unitialized last_out */
    if (last_out == -1)
     last_out = 0;
    if (min_out_time == -1 || last_out < min_out_time)
    min_out_time = last_out;
  }

The problem is that last_out ends up being unitialized if the set-active signal is not emitted. I'm not sure what value should be used.

(See CID 1455443)