canvas.toBlob() Silently Falls Back to PNG on Unsupported Formats

When using canvas.toBlob() to convert images to WebP or AVIF, the method may silently return a PNG if the requested format isn't supported by the browser. This bug can mislead developers into thinking the conversion succeeded, while the output file is actually in a different format. The issue stems from the API's fallback behavior, which doesn't throw an error or warning.