reset the have_index flag at transition PAUSED_TO_READY

If we restart the Stream in the case of doing a transition from
PAUSED_TO_READY and back with READY_TO_PAUSED aso. the duration of the video
will get calculated even if we have a avi header with that information.
Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>

gst/avi/gstavidemux.c

@@ -5346,6 +5346,7 @@ gst_avi_demux_change_state (GstElement * element, GstStateChange transition)
 
   switch (transition) {
     case GST_STATE_CHANGE_PAUSED_TO_READY:
+      avi->have_index = FALSE;
       gst_avi_demux_reset (avi);
       break;
     default: