fix crash on track delete

trap/renderer.py

@@ -462,10 +462,12 @@ class Renderer:
                     self.drawn_tracks[track_id].set_track(track, self.prediction_frame.H)
         
         # clean up
-        for track in self.drawn_tracks.values():
+        for track_id in list(self.drawn_tracks.keys()):
-            if track.update_at < time.time() - 5:
+            # TODO make delay configurable
+            if self.drawn_tracks[track_id].update_at < time.time() - 5:
                 # TODO fade out
                 del self.drawn_tracks[track_id]
+
     
     def on_key_press(self, symbol, modifiers):
         print('A key was pressed, use f to hide')