Can't reuse component after drag-drop

[WoozyG]

After selecting or dropping a file on a multi-file upload set to files=1, I can't select or drop another file, it says "too many files selected." This is after handling the first file on the server and clearing the server-side component.

Somewhere, server, client, or both, is holding on to a reference to the previously uploaded file, and not replacing it on the next selection or drop event.

If that's expected, then a new reset() method or similar is needed to actually clear state so we don't have to discard and recreate the component after every upload.

This issue arose out of #25.