Fixed PNG saving.

dlib/image_saver/save_png.h

@@ -80,9 +80,9 @@ namespace dlib
 
             impl::impl_save_png(file_name, row_pointers, img.nc(), impl::png_type_rgb_alpha, 8);
         }
-        else if (pixel_traits<pixel_type>::hsi || pixel_traits<pixel_type>::rgb)
+        else if (pixel_traits<pixel_type>::lab || pixel_traits<pixel_type>::hsi || pixel_traits<pixel_type>::rgb)
         {
-            // convert from HSI to RGB (Or potentially RGB pixels that aren't laid out as R G B)
+            // convert from Lab or HSI to RGB (Or potentially RGB pixels that aren't laid out as R G B)
             array2d<rgb_pixel> temp_img;
             assign_image(temp_img, img_);
             for (unsigned long i = 0; i < row_pointers.size(); ++i)