xmlcopyeditor: fix build with libxml2 2.14 (#424381)

pkgs/by-name/xm/xmlcopyeditor/package.nix

@@ -27,10 +27,16 @@ stdenv.mkDerivation (finalAttrs: {
 
   # error: cannot initialize a variable of type 'xmlErrorPtr' (aka '_xmlError *')
   #        with an rvalue of type 'const xmlError *' (aka 'const _xmlError *')
-  postPatch = ''
-    substituteInPlace src/wraplibxml.cpp \
-      --replace-fail "xmlErrorPtr err" "const xmlError *err"
-  '';
+  postPatch =
+    ''
+      substituteInPlace src/wraplibxml.cpp \
+        --replace-fail "xmlErrorPtr err" "const xmlError *err"
+    ''
+    # error: invalid type argument of unary '*' (have 'long int')
+    + ''
+      substituteInPlace src/wraplibxml.cpp \
+        --replace-fail "initGenericErrorDefaultFunc ( NULL )" "xmlSetGenericErrorFunc( nullptr , nullptr )"
+    '';
 
   nativeBuildInputs = [
     intltool