Call png_image_free_function without guarding it with png_safe_execute

png_image_free_function (or any other destructor) should never fail.
Destructors need not and must not be executed under png_safe_execute.

Reference: CVE-2019-7317, use-after-free in png_image_free

png.c

@@ -4588,8 +4588,7 @@ png_image_free(png_imagep image)
    if (image != NULL && image->opaque != NULL &&
       image->opaque->error_buf == NULL)
    {
-      /* Ignore errors here: */
-      (void)png_safe_execute(image, png_image_free_function, image);
+      png_image_free_function(image);
       image->opaque = NULL;
    }
 }