bpo-32436: Fix compiler warning (GH-5483) (GH-5486)

(cherry picked from commit 55e0839f2672e029c2b96514028c77c31ffbe41f)

Co-authored-by: Yury Selivanov <yury@magic.io>
diff --git a/Python/hamt.c b/Python/hamt.c
index 8998dbd..c9acbbc 100644
--- a/Python/hamt.c
+++ b/Python/hamt.c
@@ -2358,6 +2358,8 @@
             Py_INCREF(o);
             return o;
         case W_NEWNODE: {
+            assert(new_root != NULL);
+
             PyHamtObject *new_o = hamt_alloc();
             if (new_o == NULL) {
                 Py_DECREF(new_root);