A fallback search function for "zero candidates" case.

[a13]

Sometimes when I mix up a "jumping" shortcut with the search one, or I want to jump to a word which isn't on the screen anymore, I get "zero candidates" message and avy just quits after that.

I think it could be usable to have a customizable function, which is (if not nil) called interactively using the jump char(s) as initial input (both swiper and swiper-isearch support it, not sure about helm-swoop nor the consult one, though).