Remove textures with no references

Vocaluxe/Base/CDraw.cs

@@ -177,7 +177,9 @@ namespace Vocaluxe.Base
 
         public static void RemoveTexture(ref CTextureRef texture)
         {
-            _Draw.RemoveTexture(ref texture);
+            // Disposed textures call this, possibly at program end!
+            if (_Draw != null)
+                _Draw.RemoveTexture(ref texture);
         }
 
         public static void DrawTexture(CTextureRef texture)

Vocaluxe/Lib/Draw/CDrawBase.cs

@@ -383,6 +383,7 @@ namespace Vocaluxe.Lib.Draw
                     _Textures.Remove(texture.ID);
                 }
             }
+            texture.ID = -1;
             texture = null;
         }
 

VocaluxeLib/Draw/CTextureRef.cs

@@ -24,7 +24,7 @@ namespace VocaluxeLib.Draw
     /// </summary>
     public class CTextureRef
     {
-        public readonly int ID;
+        public int ID;
 
         public string TexturePath = "";
 
@@ -115,6 +115,16 @@ namespace VocaluxeLib.Draw
             _CalcRatios();
         }
 
+        ~CTextureRef()
+        {
+            if (ID >= 0)
+            {
+                //Free textures that are no longer reference
+                CTextureRef tmp = this;
+                CBase.Drawing.RemoveTexture(ref tmp);
+            }
+        }
+
         private void _CalcRatios()
         {
             // OpenGL has a problem with partial (NPOT) textures, so we remove 1 pixel