fix(player): 优化上下滑切集黑屏

lib/pages/player/widgets/player_video_surface.dart

@@ -18,10 +18,14 @@ class PlayerVideoSurface extends StatefulWidget {
     required this.videoUrl,
     required this.theater,
     this.handoff,
+    this.openingFrame,
   });
 
   final VideoPlayerController? controller;
   final VideoPlayerController? handoff;
+
+  /// 解码出第一帧之前垫上的视频首帧，没有则为空。
+  final Widget? openingFrame;
   final String videoUrl;
   final bool theater;
 
@@ -60,6 +64,11 @@ class _PlayerVideoSurfaceState extends State<PlayerVideoSurface> {
           key: Key('player-fallback-background'),
           color: AppColors.mediaBlack,
         ),
+        if (!reveal && widget.openingFrame != null)
+          KeyedSubtree(
+            key: const Key('player-opening-frame'),
+            child: widget.openingFrame!,
+          ),
         AnimatedOpacity(
           key: const Key('player-video-opacity'),
           opacity: reveal ? 1 : 0,
@@ -99,10 +108,9 @@ class _PlayerVideoSurfaceState extends State<PlayerVideoSurface> {
   }
 
   bool _shouldReveal(VideoPlayerValue? value, bool covered) {
+    if (covered) return value?.isInitialized ?? false;
     if (value == null || value.hasError || !value.isInitialized) return false;
-    if (value.size.width <= 0) return false;
-    if (covered) return true;
-    return value.position > Duration.zero || value.isPlaying;
+    return value.size.width > 0 && value.size.height > 0;
   }
 
   /// 只画会话仍持有的旧画面，控制器一旦被换掉就不再引用。