Generate: `min_tokens_to_keep` has to be `>= 1`
# What does this PR do?

As pointed out by @njhill in [this comment](https://github.com/huggingface/transformers/pull/24111#issuecomment-1601824441), `min_tokens_to_keep` has to be `>=1`. When it is not, the sampling step will lead to numerical exceptions, as all tokens have `-float("inf")` as logits.

This PR updates some of the checks, which were checking that it was `>=0`, and fixes the typical_p logits processor, which has the exact same issue as the one fixed in https://github.com/huggingface/transformers/pull/24111
_The documentation is not available anymore as the PR was closed or merged._<|||||>Thanks @gante!