clapper: Also update decoders after preroll

Sometimes decoders might not be active yet until media starts playing, to fix that being racy also try to update them after preroll

src/lib/clapper/clapper-playbin-bus.c

@@ -613,6 +613,9 @@ _handle_state_changed_msg (GstMessage *msg, ClapperPlayer *player)
     }
 
     _update_current_duration (player);
+
+    if (!player->use_playbin3)
+      clapper_player_playbin_update_current_decoders (player);
   }
 }