Improve hq.rs

Attention: there is clearly a bug in the code when it uses `v.wrapping_add(1) > 0` when `v` is a `usize`-- because the only way for this condition to be false is for `v` to be `usize::MAX` -- and this will not be consistent between x32 and x64 versions. Moreover, there is even a case of `wrapping_add(2)` -- which would only pass if the original is `usize::MAX-1`.

Given all this, this expression does not make any sense, and should be replaced with `m.alloc_cell(num_bytes + 2)`:

```rust
if num_bytes + 2 > 0 {
    m.alloc_cell(num_bytes + 2)
} else {
    AllocF::AllocatedMemory::default()
}
```

Author: nyurik