do not play bg music files twice until all files are played

Vocaluxe/Base/CBackgroundMusic.cs

@@ -16,6 +16,7 @@ namespace Vocaluxe.Base
         private static string _CurrentMusicFilePath = String.Empty;
         
         private static List<string> _AllFileNames = new List<string>();
+        private static List<string> _NotPlayedFileNames = new List<string>();
         private static List<string> _BGMusicFileNames = new List<string>();
         
         private static bool _OwnMusicAdded;
@@ -84,7 +85,12 @@ namespace Vocaluxe.Base
             {
                 Stop();
 
-                _CurrentMusicFilePath = _AllFileNames[CGame.Rand.Next(_AllFileNames.Count)];
+                if (_NotPlayedFileNames.Count == 0)
+                    _NotPlayedFileNames.AddRange(_AllFileNames);
+
+                _CurrentMusicFilePath = _NotPlayedFileNames[CGame.Rand.Next(_NotPlayedFileNames.Count)];
+                _NotPlayedFileNames.Remove(_CurrentMusicFilePath);
+
                 _CurrentMusicStream = CSound.Load(_CurrentMusicFilePath);
                 CSound.SetStreamVolume(_CurrentMusicStream, 0f);
                 Play();
@@ -105,6 +111,7 @@ namespace Vocaluxe.Base
                 foreach (CSong song in CSongs.AllSongs)
                 {
                     _AllFileNames.Add(song.GetMP3());
+                    _NotPlayedFileNames.Add(song.GetMP3());
                 }
             }
             _OwnMusicAdded = true;
@@ -113,9 +120,13 @@ namespace Vocaluxe.Base
         public static void RemoveOwnMusic()
         {
             _AllFileNames.Clear();
+            _NotPlayedFileNames.Clear();
 
             if (_BackgroundMusicAdded)
+            {
                 _AllFileNames.AddRange(_BGMusicFileNames);
+                _NotPlayedFileNames.AddRange(_BGMusicFileNames);
+            }
 
             if (IsPlaying() && !IsBackgroundFile(_CurrentMusicFilePath) || _AllFileNames.Count == 0)
                 Next();
@@ -128,6 +139,7 @@ namespace Vocaluxe.Base
             if (!_BackgroundMusicAdded)
             {
                 _AllFileNames.AddRange(_BGMusicFileNames);
+                _NotPlayedFileNames.AddRange(_BGMusicFileNames);
                 _BackgroundMusicAdded = true;
             }
         }