Fix hashtable del bug

src/hashtable.c

@@ -145,7 +145,7 @@ int hashtable_del(hashtable *ht, char *key) {
             && !strncmp(key, current->key, key_size)) {
             prev->next = current->next;
             if (current == ht->buckets[bucket]) {
-               ht->buckets[bucket] = NULL;
+               ht->buckets[bucket] = prev;
             }
             free(current->key);
             ht->free ? ht->free(current->value):free(current->value);