Bail out early with message if Lookup is called on non-directory node.

fuse/fsops.go

@@ -50,6 +50,10 @@ func (me *FileSystemConnector) internalLookup(parent *Inode, name string, contex
 
 func (me *FileSystemConnector) Lookup(header *InHeader, name string) (out *EntryOut, code Status) {
 	parent := me.toInode(header.NodeId)
+	if !parent.IsDir() {
+		log.Printf("Lookup %q called on non-Directory node %d", name, header.NodeId) 
+		return nil, ENOTDIR
+	}
 	context := &header.Context
 	fi, child, code := me.internalLookup(parent, name, context)
 	if !code.Ok() {