Fix audio processing edge case

[ZachNagengast]

Resolves #228

This is a case where the framePosition of the AVAudioFile is not actually correctly being set after reaching the end of the file. For some reason, the frame count does not match the actual frame count of the file. However, reading the file still works even if it is told to read more frames than exist in the file, so we will track the frame position ourselves and stop trying to read the file after we have reached what we think is the end of the file, even if less frames have been returned. It appears to be an internal Apple bug.

[Josscii]

Hi, I found this bug could be fixed by detecting the bad file and convert it to m4a.

In my transcribe code, I always try init a AVAudioFile, if it failed, I use AVAssetExportSession to convert it to a m4a, and then do the transcribe, because the bad file like this one.

var audioFile = try? AVAudioFile(forReading: fileURL)

if audioFile == nil || task.retry {
    let url = await AudioExporter.tryExport(url: fileURL, filename: "transcribe_temp")
    if Task.isCancelled {
        return false
    }

    if let url {
        fileURL = url
        audioFile = try AVAudioFile(forReading: fileURL)
    }
}

After converting it, it works ok with the original code.

An another possible solution to this bug.