fix(player): 修复进度条拖动树稳定性

lib/pages/player/player_view.dart

@@ -304,11 +304,13 @@ class _PlayerPageState extends State<PlayerPage>
   }
 
   void _setScrubbing(bool value) {
+    if (!mounted) return;
     if (_scrubbing == value) return;
     setState(() => _scrubbing = value);
   }
 
   void _finishFeedScrub(bool wasVisible) {
+    if (!mounted) return;
     setState(() {
       _scrubbing = false;
       _chromeVisible = wasVisible;
@@ -322,6 +324,7 @@ class _PlayerPageState extends State<PlayerPage>
   }
 
   void _restoreFeedChrome() {
+    if (!mounted) return;
     setState(() {
       _scrubbing = false;
       _chromeVisible = true;