Fix CVE-2017-8105:

https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2017-8105
https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=935

Patch copied from upstream source repository:

https://git.savannah.gnu.org/cgit/freetype/freetype2.git/commit/?id=f958c48ee431bef8d4d466b40c9cb2d4dbcb7791

From f958c48ee431bef8d4d466b40c9cb2d4dbcb7791 Mon Sep 17 00:00:00 2001
From: Werner Lemberg <wl@gnu.org>
Date: Fri, 24 Mar 2017 09:15:10 +0100
Subject: [PATCH] [psaux] Better protect `flex' handling.

Reported as

  https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=935

* src/psaux/t1decode.c (t1_decoder_parse_charstrings)
<callothersubr>: Since there is not a single flex operator but a
series of subroutine calls, malformed fonts can call arbitrary other
operators after the start of a flex, possibly adding points.  For
this reason we have to check the available number of points before
inserting a point.
---
 ChangeLog            | 15 +++++++++++++++
 src/psaux/t1decode.c |  9 +++++++++
 2 files changed, 24 insertions(+)

diff --git a/src/psaux/t1decode.c b/src/psaux/t1decode.c
index af7b465e..7dd45135 100644
--- a/src/psaux/t1decode.c
+++ b/src/psaux/t1decode.c
@@ -780,10 +780,19 @@
             /* point without adding any point to the outline    */
             idx = decoder->num_flex_vectors++;
             if ( idx > 0 && idx < 7 )
+            {
+              /* in malformed fonts it is possible to have other */
+              /* opcodes in the middle of a flex (which don't    */
+              /* increase `num_flex_vectors'); we thus have to   */
+              /* check whether we can add a point                */
+              if ( FT_SET_ERROR( t1_builder_check_points( builder, 1 ) ) )
+                goto Syntax_Error;
+
               t1_builder_add_point( builder,
                                     x,
                                     y,
                                     (FT_Byte)( idx == 3 || idx == 6 ) );
+            }
           }
           break;
 
-- 
2.12.2

