Fix code review issues: improve efficiency and null safety

Co-authored-by: YBTopaz8 <41630728+YBTopaz8@users.noreply.github.com>

Author: Copilot

Dimmer/Dimmer.WinUI/Views/WinuiPages/AllSongsListPage.xaml.cs

@@ -1399,7 +1399,6 @@ private void SelectedSongImg_Loaded(object sender, RoutedEventArgs e)
     private void ShowNotification(string message, Microsoft.UI.Xaml.Controls.InfoBarSeverity severity)
     {
         // Use a TeachingTip or create a temporary InfoBar for notifications
-        // For now, we'll use a simple ContentDialog approach or you can add an InfoBar to the XAML
         DispatcherQueue.TryEnqueue(() =>
         {
             var infoBar = new Microsoft.UI.Xaml.Controls.InfoBar
@@ -1417,15 +1416,17 @@ private void ShowNotification(string message, Microsoft.UI.Xaml.Controls.InfoBar
                 infoBar.IsOpen = false;
                 timer.Stop();
                 // Remove from visual tree after closing animation
-                var parentPanel = infoBar.Parent as Panel;
-                parentPanel?.Children.Remove(infoBar);
+                if (infoBar.Parent is Panel parentPanel)
+                {
+                    parentPanel.Children.Remove(infoBar);
+                }
             };
 
-            // Add to the page's main grid (assuming there's a Grid named MyPageGrid)
-            if (MyPageGrid is Grid grid && grid.Children.Count > 0)
+            // Add to the page's main grid
+            if (MyPageGrid != null)
             {
                 // Insert at the top of the grid
-                grid.Children.Insert(0, infoBar);
+                MyPageGrid.Children.Insert(0, infoBar);
                 timer.Start();
             }
         });

Dimmer/Dimmer/ViewModel/BaseViewModel.cs

@@ -3846,7 +3846,16 @@ public async Task PlaySongWithActionAsync(
     private async Task PlaySongNextAsync(SongModelView songToPlay)
     {
         // Check if the song is already in the current queue
-        int existingIndex = _playbackQueue.ToList().FindIndex(s => s.Id == songToPlay.Id);
+        int existingIndex = -1;
+        for (int i = 0; i < _playbackQueue.Count; i++)
+        {
+            if (_playbackQueue[i].Id == songToPlay.Id)
+            {
+                existingIndex = i;
+                break;
+            }
+        }
+        
         if (existingIndex != -1 && _playbackQueue.Count > 0)
         {
             // Song is already in queue, jump to it instead of adding again