Qwen3-ASR mishandles invalid, short, and no-speech audio inputs

Problem

Qwen3-ASR preprocessing loses the distinction between invalid or short input and mlx-audio's default min_chunk_duration=1.0 padding:

• A zero-frame array is padded and sent to the model, which can hallucinate text.
• NaN and infinite samples are not rejected before preprocessing.
• A valid 10 ms clip is reported with a 1.0-second segment end after padding.
• An empty language None<asr_text> response exposes the literal language None instead of an empty no-speech result.
• Auto-detected language from one chunk is reused as the request for later chunks, so a silent chunk can corrupt following transcription.

Expected behavior

• Reject empty and non-finite Qwen3-ASR audio before inference.
• Keep minimum-length padding for valid short clips, but report their original duration.
• Parse language None<asr_text> as empty language and text.
• Keep automatic language detection independent for every chunk.

A real-model check reproduced the empty-input hallucination and padded duration. Tested on current main at 246e233.