bpo-33803: Fix a crash in hamt.c (GH-7504) (GH-7505)

(cherry picked from commit 378c53cc3187dba57c7560ccc2557f516c8a7bc8)

Co-authored-by: Yury Selivanov <yury@magic.io>
diff --git a/Python/hamt.c b/Python/hamt.c
index 5217122..f8bce59 100644
--- a/Python/hamt.c
+++ b/Python/hamt.c
@@ -2476,6 +2476,8 @@
     if (o == NULL) {
         return NULL;
     }
+    o->h_count = 0;
+    o->h_root = NULL;
     o->h_weakreflist = NULL;
     PyObject_GC_Track(o);
     return o;