If a line inside .Bl -column starts with a tab character

and there was no preceding .It macro, do not read the byte
before the beginning of the line buffer.
Found by tb@ with afl@.

diff --git a/usr.bin/mandoc/mdoc_argv.c b/usr.bin/mandoc/mdoc_argv.c
index 4ea7b4d..705256c 100644 (file)
--- a/usr.bin/mandoc/mdoc_argv.c
+++ b/usr.bin/mandoc/mdoc_argv.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: mdoc_argv.c,v 1.64 2016/07/15 18:02:32 schwarze Exp $ */
+/*     $OpenBSD: mdoc_argv.c,v 1.65 2016/08/28 16:13:51 schwarze Exp $ */
 /*
  * Copyright (c) 2008, 2009, 2010, 2011 Kristaps Dzonsons <kristaps@bsd.lv>
  * Copyright (c) 2012, 2014, 2015 Ingo Schwarze <schwarze@openbsd.org>
@@ -478,7 +478,7 @@ args(struct roff_man *mdoc, int line, int *pos,
                         * unless there is a blank in between.
                         */
 
-                       if (p[-1] != ' ')
+                       if (p > buf && p[-1] != ' ')
                                mdoc->flags |= MDOC_PHRASEQL;
                        if (p[1] != ' ')
                                mdoc->flags |= MDOC_PHRASEQN;