Use-after-free detected with static analysis.

CVE: CVE-2019-7317
Upstream-Status: Submitted [https://github.com/glennrp/libpng/issues/275]
Signed-off-by: Ross Burton <ross.burton@intel.com>

diff --git a/png.c b/png.c
index 9d9926f638..efd1aecfbd 100644
--- a/png.c
+++ b/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;
    }
 }