hashtable: add bounds check in hashtableNext iterator

Prevent iteration beyond hashtable bounds by checking if iterator
is already at the end before proceeding with the main iteration loop.
This adds defensive bounds checking for table index and bucket index.

Author: uriyage

src/hashtable.c

@@ -2025,6 +2025,14 @@ void hashtableReleaseIterator(hashtableIterator *iterator) {
  * Returns false if there are no more entries. */
 bool hashtableNext(hashtableIterator *iterator, void **elemptr) {
     iter *iter = iteratorFromOpaque(iterator);
+    /*  Check if iterator is already at the end */
+    if (iter->table > 1 ||
+        (iter->table == 1 && !hashtableIsRehashing(iter->hashtable)) ||
+        (iter->index >= 0 && iter->hashtable->tables[iter->table] &&
+            (size_t)iter->index >= numBuckets(iter->hashtable->bucket_exp[iter->table]))) {
+        return 0;
+    }
+
     while (1) {
         if (iter->index == -1 && iter->table == 0) {
             /* It's the first call to next. */