auto select existed account when detecting

src/Snap.Hutao/Snap.Hutao/Service/Game/GameService.cs

@@ -281,7 +281,7 @@ internal sealed partial class GameService : IGameService
     }
 
     /// <inheritdoc/>
-    public async ValueTask DetectGameAccountAsync()
+    public async ValueTask<GameAccount?> DetectGameAccountAsync()
     {
         ArgumentNullException.ThrowIfNull(gameAccounts);
 
@@ -318,7 +318,11 @@ internal sealed partial class GameService : IGameService
                     gameAccounts.Add(account);
                 }
             }
+
+            return account;
         }
+
+        return default;
     }
 
     /// <inheritdoc/>

src/Snap.Hutao/Snap.Hutao/Service/Game/IGameService.cs

@@ -26,11 +26,7 @@ internal interface IGameService
     /// <param name="uid">uid</param>
     void AttachGameAccountToUid(GameAccount gameAccount, string uid);
 
-    /// <summary>
-    /// 检测并尝试添加游戏内账户
-    /// </summary>
-    /// <returns>任务</returns>
-    ValueTask DetectGameAccountAsync();
+    ValueTask<GameAccount?> DetectGameAccountAsync();
 
     /// <summary>
     /// 异步获取游戏路径

src/Snap.Hutao/Snap.Hutao/ViewModel/Game/LaunchGameViewModel.cs

@@ -236,7 +236,15 @@ internal sealed partial class LaunchGameViewModel : Abstraction.ViewModel
     {
         try
         {
-            await gameService.DetectGameAccountAsync().ConfigureAwait(false);
+            GameAccount? account = await gameService.DetectGameAccountAsync().ConfigureAwait(false);
+
+            // If user canceled the operation, the return is null,
+            // and thus we should not set SelectedAccount
+            if (account is not null)
+            {
+                await taskContext.SwitchToMainThreadAsync();
+                SelectedGameAccount = account;
+            }
         }
         catch (UserdataCorruptedException ex)
         {