Fix the exit code for the case where nentries == 0; if a PID doesn't exist,

ps(1) should not be returning a success code (0), it should return an
error code (1).  This was fixed on OpenBSD over 3 years ago.

PR:		19069
Submitted by:	Jim Sloan <odinn@atlantabiker.net>
Reviewed by:	rwatson

bin/ps/ps.c

@@ -355,7 +355,7 @@ main(argc, argv)
 	 */
 	printheader();
 	if (nentries == 0)
-		exit(0);
+		exit(1);
 	/*
 	 * sort proc list
 	 */