graphviz: 2.40.1 -> 2.42.2

Little uncertain what's going on re:versions,
here's some info:

2.42.0 "Fixes quite a few bugs"[1], which is primary motivation.

[1] https://gitlab.com/graphviz/graphviz/blob/stable_release_2.42.0/ChangeLog

2.42.1 has a note in 2.42.2's ChangeLog[2] which is good but also
interesting as 2.42.2 doesn't have an entry in its own ChangeLog :).
FWIW there are two tags for 2.42.2 but happily they're equivalent.

While a bit verbose, the changes between these versions can be looked at
using git locally or a URL like one of these:

* https://gitlab.com/graphviz/graphviz/compare/stable_release_2.42.0...stable_release_2.42.2
* https://gitlab.com/graphviz/graphviz/compare/stable_release_2.40.1...stable_release_2.42.0

Anyway, looks like a bunch of bugfixes! :)

pkgs/tools/graphics/graphviz/base.nix

@@ -7,7 +7,7 @@
 assert stdenv.isDarwin -> ApplicationServices != null;
 
 let
-  inherit (stdenv.lib) optionals optionalString;
+  inherit (stdenv.lib) optional optionals optionalString;
   raw_patch =
     # https://gitlab.com/graphviz/graphviz/issues/1367 CVE-2018-10196
     fetchpatch {
@@ -17,11 +17,13 @@ let
       excludes = ["tests/*"]; # we don't run them and they don't apply
     };
   # the patch needs a small adaption for older versions
-  patch = if stdenv.lib.versionAtLeast version "2.37" then raw_patch else
+  patchToUse = if stdenv.lib.versionAtLeast version "2.37" then raw_patch else
   stdenv.mkDerivation {
     inherit (raw_patch) name;
     buildCommand = "sed s/dot_root/agroot/g ${raw_patch} > $out";
   };
+  # 2.42 has the patch included
+  patches = optional (stdenv.lib.versionOlder version "2.42") patchToUse;
 in
 
 stdenv.mkDerivation {
@@ -52,9 +54,7 @@ stdenv.mkDerivation {
     "--with-ltdl-include=${libtool}/include"
   ] ++ stdenv.lib.optional (xorg == null) [ "--without-x" ];
 
-  patches = [
-    patch
-  ];
+  inherit patches;
 
   postPatch = ''
     for f in $(find . -name Makefile.in); do