Fix CVE-2017-14685:

https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2017-14685

Patch copied from upstream source repository:

https://git.ghostscript.com/?p=mupdf.git;h=ab1a420613dec93c686acbee2c165274e922f82a

From ab1a420613dec93c686acbee2c165274e922f82a Mon Sep 17 00:00:00 2001
From: Tor Andersson <tor.andersson@artifex.com>
Date: Tue, 19 Sep 2017 15:23:04 +0200
Subject: [PATCH] Fix 698539: Don't use xps font if it could not be loaded.

xps_load_links_in_glyphs did not cope with font loading failures.
---
 source/xps/xps-link.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/source/xps/xps-link.c b/source/xps/xps-link.c
index c07e0d7..c26a8d9 100644
--- a/source/xps/xps-link.c
+++ b/source/xps/xps-link.c
@@ -91,6 +91,8 @@ xps_load_links_in_glyphs(fz_context *ctx, xps_document *doc, const fz_matrix *ct
 			bidi_level = atoi(bidi_level_att);
 
 		font = xps_lookup_font(ctx, doc, base_uri, font_uri_att, style_att);
+		if (!font)
+			return;
 		text = xps_parse_glyphs_imp(ctx, doc, &local_ctm, font, fz_atof(font_size_att),
 				fz_atof(origin_x_att), fz_atof(origin_y_att),
 				is_sideways, bidi_level, indices_att, unicode_att);
-- 
2.9.1

