Stop coredump on Solaris if arg not specified (Jason Kau - 1465288)

git-svn-id: https://nagiosplug.svn.sourceforge.net/svnroot/nagiosplug/nagiosplug/trunk@1370 f882894a-f735-0410-b71e-b25c423dba1c

THANKS.in

@@ -180,3 +180,4 @@ Johan Fischer
 Sakari Lehtonen
 John Rouillard
 Sebastian Wiesinger
+Jason Kau

plugins/utils.c

@@ -71,7 +71,7 @@ void usage_va (const char *fmt, ...)
 
 void usage2(const char *msg, const char *arg)
 {
-	printf ("%s: %s - %s\n",progname,msg,arg);
+	printf ("%s: %s - %s\n", progname, msg, arg?arg:"(null)" );
 	print_usage ();
 	exit (STATE_UNKNOWN);
 }