libsixel: update to 1.8.5. (security update)

Upstream changes (from NEWS):

v1.8.5

* Security fix for CVE-2019-20205 (#127), integer overflow problem,
  reported by @sleicasper.

* Security fix for CVE-2019-20056 (#126), assertion failure problem,
  reported by @sleicasper.

* Security fix for CVE-2019-20094 (#125), heap overflow problem,
  reported by @cuanduo.

* Security fix for #124, illegal longjump() call problem,
  reported by @cuanduo.

* Serucity fix for #74 and #123, access violation problem,
  reported by @hongxuchen and SuhwanSong.

* Security fix for #122, heap overflow problem,
  reported by @SuhwanSong.

* Security fix for CVE-2019-20023(#117, #119, #120), memory leaks problem,
  reported by @SuhwanSong and @gutiniao.

* Strip first flag check in LZW compression function for issue #118,
  reported by @yoichi

graphics/libsixel/Makefile

@@ -1,6 +1,6 @@
-# $NetBSD: Makefile,v 1.44 2019/12/22 02:58:32 tsutsui Exp $
+# $NetBSD: Makefile,v 1.45 2020/01/03 01:51:01 tsutsui Exp $
 
-DISTNAME=		libsixel-1.8.4
+DISTNAME=		libsixel-1.8.5
 CATEGORIES=		graphics
 MASTER_SITES=		${MASTER_SITE_GITHUB:=saitoha/}
 GITHUB_PROJECT=		libsixel

graphics/libsixel/distinfo

@@ -1,6 +1,6 @@
-$NetBSD: distinfo,v 1.23 2019/12/22 02:58:32 tsutsui Exp $
+$NetBSD: distinfo,v 1.24 2020/01/03 01:51:01 tsutsui Exp $
 
-SHA1 (libsixel-1.8.4.tar.gz) = fc1e200c551119d3ab01162ac7cdbb8df809b8d6
-RMD160 (libsixel-1.8.4.tar.gz) = c6660e565361e2ed150feb48d0538cc20b4aca9a
-SHA512 (libsixel-1.8.4.tar.gz) = 20bbc9d6ecbc7a27064a391d066d604fd2ff437a6d429288c36287e314104ff4d1e7f2f4e09a0e62ab0fc68bde34e47d17f3a00f285afd1859a685d14d97c2e4
-Size (libsixel-1.8.4.tar.gz) = 4782947 bytes
+SHA1 (libsixel-1.8.5.tar.gz) = 78f6a145de81d7714755eda8955fd334158f206b
+RMD160 (libsixel-1.8.5.tar.gz) = 2a56d2a8bb1ff592784b6dc53ea282a5d776816e
+SHA512 (libsixel-1.8.5.tar.gz) = 6cfe271e0fba985125ea7925d96bff25b9100621cbca946deeebfdfd8128fb0e0fb2d2b5506c018b526b1af9c15ee25fdbfd4b9ba97bac4f1ee8f4d629ba5ed5
+Size (libsixel-1.8.5.tar.gz) = 4790776 bytes