Editor: replaced few incorrect uses of GetSpriteBitmapAs32Bit()

This fixes:
- Sprite export
- Copy sprite to clipboard
- Recreate spritefile

in case any sprite is non-32 bit.

Editor/AGS.Editor/Panes/SpriteSelector.cs

@@ -782,7 +782,7 @@ private void SpriteContextMenuEventHandler(object sender, EventArgs e)
  else if (item.Name == MENU_ITEM_COPY_TO_CLIPBOARD)
  {
  Sprite sprite = FindSpriteByNumber(_spriteNumberOnMenuActivation);
- Bitmap bmp = Factory.NativeProxy.GetSpriteBitmapAs32Bit(sprite.Number, sprite.Width, sprite.Height);
+ Bitmap bmp = Factory.NativeProxy.GetSpriteBitmap(sprite.Number);
 
  if (GetDesktopColourDepth() < 32 &&
  (bmp.PixelFormat == PixelFormat.Format32bppArgb || bmp.PixelFormat == PixelFormat.Format32bppRgb))
@@ -1175,7 +1175,7 @@ private void CropSelectedSprites(bool symettric)
 
  private void ExportSprite(string fileName, Sprite sprite)
  {
- Bitmap bmp = Factory.NativeProxy.GetSpriteBitmapAs32Bit(sprite.Number, sprite.Width, sprite.Height);
+ Bitmap bmp = Factory.NativeProxy.GetSpriteBitmap(sprite.Number);
  ImportExport.ExportBitmapToFile(fileName, bmp);
  bmp.Dispose();
  }

Editor/AGS.Editor/Utils/SpriteTools.cs

@@ -463,7 +463,7 @@ public static void ExportSprite(Sprite sprite, string path, bool updateSourcePat
  }
 
  ImageFormat format = sprite.ColorDepth < 32 && !sprite.AlphaChannel ? ImageFormat.Bmp : ImageFormat.Png;
- Bitmap bmp = Factory.NativeProxy.GetSpriteBitmapAs32Bit(sprite.Number, sprite.Width, sprite.Height);
+ Bitmap bmp = Factory.NativeProxy.GetSpriteBitmap(sprite.Number);
  path = string.Format("{0}.{1}", path, format.ToString().ToLower());
  bmp.Save(path, format);
  bmp.Dispose();
@@ -678,7 +678,7 @@ public static void WriteSpriteFileFromSources(string filename, IWorkProgress pro
  var bmp = LoadBitmapFromSource(sprite);
  // TODO: this is quite suboptimal, find a way to retrieve a native handle instead?
  if (bmp == null)
- bmp = Factory.NativeProxy.GetSpriteBitmapAs32Bit(sprite.Number, sprite.Width, sprite.Height);
+ bmp = Factory.NativeProxy.GetSpriteBitmap(sprite.Number);
 
  if (bmp != null)
  {