Btrfs: Fix ordering of key field checks in btrfs_previous_item

Check objectid of item before checking the item type, otherwise we may return
zero for a key that is actually too low.

Signed-off-by: Yan Zheng <zheng.yan@oracle.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

fs/btrfs/ctree.c

@@ -4296,10 +4296,10 @@ int btrfs_previous_item(struct btrfs_root *root,
 			path->slots[0]--;
 
 		btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0]);
-		if (found_key.type == type)
-			return 0;
 		if (found_key.objectid < min_objectid)
 			break;
+		if (found_key.type == type)
+			return 0;
 		if (found_key.objectid == min_objectid &&
 		    found_key.type < type)
 			break;