Fixup for rBac58a7fa (HSV doversion)

We are not bumping file version, but we cannot have the doversion code running twice.
In this particular case it was crashing files, since we were setting node->storage to NULL, and later on accessing it.

source/blender/blenloader/intern/versioning_270.c

@@ -216,6 +216,10 @@ static void anim_change_prop_name(FCurve *fcu,
 
 static void do_version_hue_sat_node(bNodeTree *ntree, bNode *node)
 {
+	if (node->storage == NULL) {
+		return;
+	}
+
 	/* Make sure new sockets are properly created. */
 	node_verify_socket_templates(ntree, node);
 	/* Convert value from old storage to new sockets. */