Allow the last entry to be picked in random song/category selection (#903)

Random.Next(min, max) excludes max, so Next(0, Count - 1) never returned
the last index. The last song or category in the list was only picked
once it was the only one left, so it always came last.

Use Next(0, Count) instead.

Co-authored-by: Florian Ostertag <flokuep@users.noreply.github.com>

Vocaluxe/Base/CSongs.cs

@@ -247,7 +247,7 @@ namespace Vocaluxe.Base
                 return -1;
             }
 
-            var song = _SongsForRandom[CGame.Rand.Next(0, _SongsForRandom.Count - 1)];
+            var song = _SongsForRandom[CGame.Rand.Next(0, _SongsForRandom.Count)];
             _SongsForRandom.Remove(song);
             return GetVisibleSongNumber(song.Id);
         }
@@ -291,7 +291,7 @@ namespace Vocaluxe.Base
                 return -1;
             }
 
-            var category = _CategoriesForRandom[CGame.Rand.Next(0, _CategoriesForRandom.Count - 1)];
+            var category = _CategoriesForRandom[CGame.Rand.Next(0, _CategoriesForRandom.Count)];
             _CategoriesForRandom.Remove(category);
             return _GetCategoryNumber(category);
         }