[fix] Clamp logprob with dtype min to prevent -inf

[ByronHsu]

Motivation

To fix #2955
Follow up #3212

The probs can have 0 and after torch.log it becomes -inf, making fastapi not able to construct response #2955.

This PR adds a clamp (https://pytorch.org/docs/stable/type_info.html) based on dtype to prevent -inf.

Modifications

Checklist

• Format your code according to the Code Formatting with Pre-Commit.
• Add unit tests as outlined in the Running Unit Tests.
• Update documentation / docstrings / example tutorials as needed, according to Writing Documentation.
• Provide throughput / latency benchmark results and accuracy evaluation results as needed, according to Benchmark and Profiling.