search get null when str2 = str1 + '\0'

after insert "1", "2", "1\0\1", we'll get null if we search  "1\0\1"。


```  
void* reproduce_issue() {
  art_tree tree;
  art_tree_init(&tree);
  int v1 = 1;
  int v2 = 2;
  int v3 = 3;
  
  art_insert(&tree, "1", 1, &v1);
  art_insert(&tree, "2", 1, &v2);
  art_insert(&tree, "1\0\1", 3, &v3);
  int* ret = art_search(&tree, "1\0\1", 3);

  return ret;
}

```