ImageMagick6: Disable ghostscript coders by default in policy.xml

Disable ghostscript coders in policy.xml as a workaround for
VU#332928 (<https://www.kb.cert.org/vuls/id/332928>).

Please note that apart commenting/removing lines added in policy.xml,
the ghostscript coders can be enabled per-user by copying policy.xml
to ~/.config/ImageMagick/policy.xml and adjusting it with the
following lines:

  | [...]
  | <policy domain="coder" rights="read|write" pattern="PS" />
  | <policy domain="coder" rights="read|write" pattern="EPS" />
  | <policy domain="coder" rights="read|write" pattern="PDF" />
  | <policy domain="coder" rights="read|write" pattern="XPS" />
  | [...]

Bump PKGREVISION

Index: Makefile
===================================================================
RCS file: /cvsroot/pkgsrc/graphics/ImageMagick6/Makefile,v
retrieving revision 1.17
diff -u -p -r1.17 Makefile
--- Makefile	22 Aug 2018 09:45:10 -0000	1.17
+++ Makefile	22 Aug 2018 13:24:32 -0000
@@ -1,6 +1,6 @@
 # $NetBSD: Makefile,v 1.17 2018/08/22 09:45:10 wiz Exp $
 
-PKGREVISION= 3
+PKGREVISION= 4
 .include "Makefile.common"
 
 PKGNAME=	ImageMagick6-${DISTVERSION}
Index: distinfo
===================================================================
RCS file: /cvsroot/pkgsrc/graphics/ImageMagick6/distinfo,v
retrieving revision 1.9
diff -u -p -r1.9 distinfo
--- distinfo	12 Mar 2018 15:47:00 -0000	1.9
+++ distinfo	22 Aug 2018 13:24:32 -0000
@@ -5,3 +5,4 @@ RMD160 (ImageMagick-6.9.9-38.tar.xz) = 5
 SHA512 (ImageMagick-6.9.9-38.tar.xz) = 78ecb605d2ea529603bab723c284be9c03a7d370814bbe708c2c34e0b91f75c1a0c193a5a2ea8f3583019d3610ac08d0d28671d8fdb2df2478865d9ab7417b91
 Size (ImageMagick-6.9.9-38.tar.xz) = 8913864 bytes
 SHA1 (patch-Makefile.in) = bb747b5e062f2a59e307289b5b33861dd5f96ab0
+SHA1 (patch-config_policy.xml) = 2b7e37cc8fedb0d06502ba1d7e65a5aea9d6ec96
Index: patches/patch-config_policy.xml
===================================================================
RCS file: patches/patch-config_policy.xml
diff -N patches/patch-config_policy.xml
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ patches/patch-config_policy.xml	22 Aug 2018 13:24:32 -0000
@@ -0,0 +1,22 @@
+$NetBSD$
+
+Disable ghostscript coders by default to workaround VU#332928:
+<https://www.kb.cert.org/vuls/id/332928>
+
+--- config/policy.xml.orig	2018-08-13 11:05:28.000000000 +0000
++++ config/policy.xml
+@@ -74,4 +74,14 @@
+   <!-- <policy domain="cache" name="memory-map" value="anonymous"/> -->
+   <!-- <policy domain="cache" name="synchronize" value="True"/> -->
+   <!-- <policy domain="cache" name="shared-secret" value="passphrase" stealth="true"/> -->
++
++  <!-- 
++    -- Disable ghostscript coders as suggested by VU#332928
++    --  <https://www.kb.cert.org/vuls/id/332928>
++    -->
++  <policy domain="coder" rights="none" pattern="PS" />
++  <policy domain="coder" rights="none" pattern="EPS" />
++  <policy domain="coder" rights="none" pattern="PDF" />
++  <policy domain="coder" rights="none" pattern="XPS" />
++
+ </policymap>