p7zip: add patch for CVE-2017-17969

patch taken from the Debian package:
https://anonscm.debian.org/cgit/users/robert/p7zip.git/tree/debian/patches/13-CVE-2017-17969.patch

Closes: #11399 [via git-merge-pr]

srcpkgs/p7zip/patches/CVE-2017-17969.patch

@@ -0,0 +1,26 @@
+From: =?utf-8?q?Antoine_Beaupr=C3=A9?= <anarcat@debian.org>
+Date: Sun, 28 Jan 2018 21:19:50 +0100
+Subject: backport of the CVE-2017-17969 fix from 7zip 18.00-beta
+
+---
+ CPP/7zip/Compress/ShrinkDecoder.cpp | 7 ++++++-
+ 1 file changed, 6 insertions(+), 1 deletion(-)
+
+diff --git a/CPP/7zip/Compress/ShrinkDecoder.cpp b/CPP/7zip/Compress/ShrinkDecoder.cpp
+index 80b7e67..4acdce5 100644
+--- CPP/7zip/Compress/ShrinkDecoder.cpp
++++ CPP/7zip/Compress/ShrinkDecoder.cpp
+@@ -121,7 +121,12 @@ HRESULT CDecoder::CodeReal(ISequentialInStream *inStream, ISequentialOutStream *
+     {
+       _stack[i++] = _suffixes[cur];
+       cur = _parents[cur];
+-    }
++      if (i >= kNumItems)
++        break;
++     }
++
++    if (i >= kNumItems)
++      break;
+     
+     _stack[i++] = (Byte)cur;
+     lastChar2 = (Byte)cur;

srcpkgs/p7zip/template

@@ -1,7 +1,7 @@
 # Template file for 'p7zip'
 pkgname=p7zip
 version=16.02
-revision=2
+revision=3
 wrksrc="${pkgname}_${version}"
 hostmakedepends="yasm nasm"
 short_desc="Command-line version of the 7zip compressed file archive"