prevent a NULL deref in an error path of got.c's diff_trees()
diff --git a/got/got.c b/got/got.c
index 2f092a4..2062852 100644
--- a/got/got.c
+++ b/got/got.c
@@ -1422,7 +1422,8 @@ diff_trees(struct got_object_id *tree_id1, struct got_object_id *tree_id2,
done:
if (tree1)
got_object_tree_close(tree1);
- got_object_tree_close(tree2);
+ if (tree2)
+ got_object_tree_close(tree2);
return err;
}