chmod: Use DIRFIRST

Previously, running `chmod 777` on a directory that had no read or
execute access (e.g. 111 or 000) would cause chmod to throw its
toys since it was trying to opendir before having added read permission
to the directory.

chmod.c

@@ -32,7 +32,7 @@ int
 main(int argc, char *argv[])
 {
 	struct recursor r = { .fn = chmodr, .hist = NULL, .depth = 0, .maxdepth = 1,
-	                      .follow = 'P', .flags = 0 };
+	                      .follow = 'P', .flags = DIRFIRST };
 	size_t i;
 
 	argv0 = *argv, argv0 ? (argc--, argv++) : (void *)0;