Adding flat option to EAN13 format not working when define the value option in the HTML element

Adding flat option to EAN13 format not working when define the value option in the HTML element.

```html

Barcode1:

Barcode2:

Barcode3:

Barcode4:

JsBarcode("#barcode1", "012345678901", {
format: "ean13",
flat: true
});
JsBarcode(".barcode").init();

```

Reproduce the four HTML examples with JsBarcode.all.js and the JsBarcode(".barcode").init() entry point, comparing the inline flat and jsbarcode-flat attributes when jsbarcode-value is provided. Trace how those attributes are read and confirm that the EAN13 barcode renders with the flat option in the HTML-driven cases.

Written by the indexing model from the issue text.