Fix segmentation fault when showing help text.

Found when running dvbv5-scan (part of coming v4l-utils upgrade).

Backtrace:
#0 hol_entry_help (entry=0x8007e0000, state=0x0, stream=0x8007d3000,
       hhstate=0x7fffffffe5d8) at argp-help.c:1164
#1 hol_help (hol=0x8007df000, state=0x0, stream=0x8007d3000) at argp-help.c:1230
#2 _help (argp=0x7fffffffe750, state=0x0, stream=0x8004fca20, flags=634,
       name=0x2018ce "dvbv5-scan") at argp-help.c:1675
#3 argp_help (argp=0x7fffffffe750, stream=0x8004fca20, flags=634,
       name=0x2018ce "dvbv5-scan") at argp-help.c:1707

Upstream maintainer has been notified.

Approved by:	pi (implicit)

devel/argp-standalone/Makefile

@@ -3,7 +3,7 @@
 
 PORTNAME=	argp-standalone
 PORTVERSION=	1.3
-PORTREVISION=	3
+PORTREVISION=	4
 CATEGORIES=	devel
 MASTER_SITES=	http://www.lysator.liu.se/~nisse/misc/ \
 		LOCAL/sem

devel/argp-standalone/files/patch-argp-help.c

@@ -0,0 +1,14 @@
+--- argp-help.c.orig	2020-04-09 17:39:48 UTC
++++ argp-help.c
+@@ -1704,7 +1704,10 @@ Try `%s --help' or `%s --usage' for more information.\
+ void __argp_help (const struct argp *argp, FILE *stream,
+ 		  unsigned flags, char *name)
+ {
+-  _help (argp, 0, stream, flags, name);
++  struct argp_state state = {
++    .root_argp = argp,
++  };
++  _help (argp, &state, stream, flags, name);
+ }
+ #ifdef weak_alias
+ weak_alias (__argp_help, argp_help)