ManUtils: Add groff instructions after running grog

Those instructions may sometimes confuse grog and cause it to autodetect
the wrong macro package.

lib/ManUtils/ManUtils.pm

@@ -24,13 +24,6 @@ sub fmt {
   $$output = '';
   @$errors = ();
 
-  $input =
-    # Disable hyphenation, since that screws up man page references. :-(
-     ".hy 0\n.de hy\n..\n"
-    # Emulate man-db's --nj option
-    .".na\n.de ad\n..\n"
-    .$input;
-
   $input = encode_utf8($input);
 
   # Call grog to figure out which preprocessors to use.
@@ -70,6 +63,13 @@ sub fmt {
     # grog 1.22.3 somehow loses the -P-c argument, let's make sure it's in the list.
     splice @cmd, 1, 0, '-P-c';
 
+    $input =
+      # Disable hyphenation, since that screws up man page references. :-(
+       ".hy 0\n.de hy\n..\n"
+      # Emulate man-db's --nj option
+      .".na\n.de ad\n..\n"
+      .$input;
+
     my $groff = run_cmd \@cmd,
       '<' => \$input,
       '>' => \my $fmt,