Define non-positive top_k; top_k range check

[ivanstepanovftw]

1. With --top_k 0 expected that all logits will be sampled (by top_p)
2. Range check added to prevent from resizing logits more than vocab have. Resizing to more than vocab have causes token 0 to be appended to logits to be sampled

[Piezoid]

@ivanstepanovftw @ggerganov
Correct me if I'm mistaken, but I think the top_p filter needs the logits to be sorted. With this PR, disabling the top_k filter bypasses the sorting.

Instead, the whole array should be sorted when there is no top_k filtering:

sample_top_k(logits_id, top_k > 0 ? std::min(top_k, n_logits) : n_logits);

[ivanstepanovftw]

You are right!