ls: check for the index size before using it in visit()

Thanks to k0ga for noticing it!
diff --git a/ls.c b/ls.c
index e55c7c5..7c97558 100644
--- a/ls.c
+++ b/ls.c
@@ -311,7 +311,7 @@
 	dev = ent->dev;
 	ino = S_ISLNK(ent->mode) ? ent->tino : ent->ino;
 
-	for (i = 0; tree[i].ino && i < PATH_MAX; ++i) {
+	for (i = 0; i < PATH_MAX && tree[i].ino; ++i) {
 		if (ino == tree[i].ino && dev == tree[i].dev)
 			return -1;
 	}