fix: make sure we are not combining chunks when only one chunk provided (#334)

## Description

<!-- Provide a concise and descriptive summary of the changes
implemented in this PR. -->
When I tried to use new whisper release I've noticed that it's for some
reason falling into infinite `generating` state.
I've done investigation and it turned out that simply I was recording
single word what was not longer than 1 chunk.
In result it was causing some silent error which prevented model from
being triggered.
This guard resolves the issue for me.


### Type of change

- [x] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to not work as expected)
- [ ] Documentation update (improves or adds clarity to existing
documentation)

### Tested on

- [x] iOS
- [ ] Android

### Testing instructions

<!-- Provide step-by-step instructions on how to test your changes.
Include setup details if necessary. -->
I cannot share the code but just simply provide very short waveform to
`transcribe` method of `useSpeechToText` hook

### Screenshots

<!-- Add screenshots here, if applicable -->
| Before | After |
| --- | --- |
| <video
src="https://github.com/user-attachments/assets/41754d72-31bb-457a-90ec-f6e4447d0fd8"
/> | <video
src="https://github.com/user-attachments/assets/03df1a87-d3c1-4ba7-8aaa-f8a47cd91613"
/> |


### Checklist

- [x] I have performed a self-review of my code
- [x] My changes generate no new warnings

### Additional notes

<!-- Include any additional information, assumptions, or context that
reviewers might need to understand this PR. -->

---------

Co-authored-by: Mateusz Kopcinski <120639731+mkopcins@users.noreply.github.com>
Co-authored-by: Mateusz Sluszniak <56299341+msluszniak@users.noreply.github.com>
Co-authored-by: Jakub Gonera <38468585+JakubGonera@users.noreply.github.com>
Co-authored-by: Norbert Klockiewicz <Nklockiewicz12@gmail.com>
Co-authored-by: pweglik <36445788+pweglik@users.noreply.github.com>

Author: 6 people

packages/react-native-executorch/src/controllers/SpeechToTextController.ts

@@ -279,6 +279,8 @@ export class SpeechToTextController {
 
   // if last chunk is too short combine it with second to last to improve quality
   private validateAndFixLastChunk() {
+    if (this.chunks.length < 2) return;
+
     const lastChunkLength = this.chunks.at(-1)!.length / SECOND;
     const secondToLastChunkLength = this.chunks.at(-2)!.length / SECOND;
     if (lastChunkLength < 5 && secondToLastChunkLength + lastChunkLength < 30) {