Don't printf("%s", NULL) if .It has a macro as an argument

in a list of a type where items don't takes arguments.
Issue found by tb@ with afl(1).

diff --git a/usr.bin/mandoc/mdoc_validate.c b/usr.bin/mandoc/mdoc_validate.c
index 68086ef..239b0d2 100644 (file)
--- a/usr.bin/mandoc/mdoc_validate.c
+++ b/usr.bin/mandoc/mdoc_validate.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: mdoc_validate.c,v 1.219 2016/08/10 12:04:57 schwarze Exp $ */
+/*     $OpenBSD: mdoc_validate.c,v 1.220 2016/08/10 12:29:02 schwarze Exp $ */
 /*
  * Copyright (c) 2008-2012 Kristaps Dzonsons <kristaps@bsd.lv>
  * Copyright (c) 2010-2016 Ingo Schwarze <schwarze@openbsd.org>
@@ -1055,10 +1055,11 @@ post_it(POST_ARGS)
                            mdoc_argnames[nbl->args->argv[0].arg]);
                /* FALLTHROUGH */
        case LIST_item:
-               if (nit->head->child != NULL)
+               if ((nch = nit->head->child) != NULL)
                        mandoc_vmsg(MANDOCERR_ARG_SKIP,
                            mdoc->parse, nit->line, nit->pos,
-                           "It %s", nit->head->child->string);
+                           "It %s", nch->string == NULL ?
+                           mdoc_macronames[nch->tok] : nch->string);
                break;
        case LIST_column:
                cols = (int)nbl->norm->Bl.ncols;