package/libxslt: add upstream security fix for CVE-2019-11068

package/libxslt: add upstream security fix for CVE-2019-11068

Fixes the following security issue:

- CVE-2019-11068: libxslt through 1.1.33 allows bypass of a protection
  mechanism because callers of xsltCheckRead and xsltCheckWrite permit
  access even upon receiving a -1 error code.  xsltCheckRead can return -1
  for a crafted URL that is not actually invalid and is subsequently loaded.

Upstream bugtracker issue not yet public:
https://gitlab.gnome.org/GNOME/libxslt/issues/12

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>