Fixed listview selected None crash

Do not use core.playback.cange_track()
close #1

mopidy_touchscreen/graphic_utils/list_view.py

@@ -87,7 +87,7 @@ class ListView():
                             self.move_to(direction)
                     else:
                         return int(key)
-        elif touch_event.type == InputManager.key:
+        elif touch_event.type == InputManager.key and self.selected is not None:
             if touch_event.direction == InputManager.enter:
                 if self.selected is not None:
                     return self.selected

mopidy_touchscreen/screens/tracklist.py

@@ -36,7 +36,7 @@ class Tracklist(BaseScreen):
     def touch_event(self, touch_event):
         pos = self.list_view.touch_event(touch_event)
         if pos is not None:
-            self.manager.core.playback.change_track(self.tracks[pos],
+            self.manager.core.playback.play(self.tracks[pos],
                                                     on_error_step=1)
 
     def track_started(self, track):