[PATCH 4/5] ui: Fix bad value for attribute action on form elements

[Jason A. Donenfeld]

Good idea with the Chrome developer tools. I just tried it myself, and
no it doesn't work.

The switch branch form works with https://git.zx2c4.com/zmusic-ng/ and
fails with https://git.zx2c4.com/zmusic-ng which is what I suspected.

It turns out action is not required either, and when omitted means
"this page", which is what we want and what I originally suggested:

https://www.w3.org/TR/html5/forms.html#attr-fs-action