Validation errors

Hi!

If I use your plugin I get two validation errors:

Bad value “” for attribute “id” on element “a”: An ID must not be the empty string.

This one is easily resolved, you just have to add an ID, but I think the attribute shouldn’t be added if it is empty to prevent this failure.

The next one is not so easy to resolve:

The “sizes” attribute may be specified only if the “srcset” attribute is also present.

This seems to be a real bug, because:

If the srcset attribute is absent, or contains no values with a width descriptor, then the sizes attribute has no effect.

https://developer.mozilla.org/en-US/docs/Web/HTML/Element/img

All the best,
Torsten