message: Don't show preserve option for alpha mapping in save dialog
diff: @@ -65,7 +65,11 @@ TextureSaveDialog::TextureSaveDialog(const TextureDescription &t, bool enableOve
  strs.clear();
  for(AlphaMapping i : values<AlphaMapping>())
  + {
  + if(i == AlphaMapping::Preserve)
  + break;
  strs << ToQStr(i);
  + }
  ui->alphaMap->addItems(strs);
  @@ -74,6 +78,9 @@ TextureSaveDialog::TextureSaveDialog(const TextureDescription &t, bool enableOve
  ui->jpegCompression->setValue(saveData.jpegQuality);
  + if(saveData.alpha == AlphaMapping::Preserve)
  + ui->alphaMap->setCurrentIndex((int)AlphaMapping::BlendToCheckerboard);
  + else
  ui->alphaMap->setCurrentIndex((int)saveData.alpha);
  ui->blackPoint->setText(Formatter::Format(saveData.comp.blackPoint));
  