RFR (S): 8079091: Remove dictionary NULL check on common path of BlockFreeList methods

[Jungwoo Ha]

Stefan, this is already reflected on webrev.03. --Jungwoo

If you want to you could remove the assert:
> -BlockFreelist::BlockFreelist() : _dictionary(NULL) {}
> +BlockFreelist::BlockFreelist()
> +    : _dictionary(new BlockTreeDictionary()) {
> +  assert(_dictionary != NULL, "Failed to allocate BlockTreeDictionary");
> +}
>
> since it's not needed.
>
> Thanks,
> StefanK
>