fix: handle RIFF padding for odd-sized WEBP chunks (#8527)

## Summary

Fix WEBP workflow loading failures for files with odd-sized chunks
before the EXIF chunk.

## Problem

WEBP files use the RIFF container format which [requires odd-sized
chunks to be padded with a single
byte](https://developers.google.com/speed/webp/docs/riff_container#riff_file_format):

> If Chunk Size is odd, a single padding byte -- which MUST be 0 to
conform with RIFF -- is added.

The `getWebpMetadata` function was not accounting for this padding,
causing it to miss the EXIF chunk in files with odd-sized preceding
chunks. This resulted in "Unable to find workflow in [filename].webp"
errors for valid WEBP files.

## Solution

Add the padding byte to the offset calculation:
```typescript
offset += 8 + chunk_length + (chunk_length % 2)
```

## Testing

- Tested with the sample image provided in the issue which previously
failed to load

Fixes #8076

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8527-fix-handle-RIFF-padding-for-odd-sized-WEBP-chunks-2fa6d73d3650815fb849fb6a4e767162)
by [Unito](https://www.unito.io)

---------

Co-authored-by: GitHub Action <action@github.com>

src/scripts/pnginfo.ts

@@ -124,7 +124,9 @@ export function getWebpMetadata(file: File) {
           break
         }
 
-        offset += 8 + chunk_length
+        // RIFF spec requires odd-sized chunks to be padded with a single byte
+        // https://developers.google.com/speed/webp/docs/riff_container#riff_file_format
+        offset += 8 + chunk_length + (chunk_length % 2)
       }
 
       r(txt_chunks)