Change to `use-dialog-box-p'

[Po Lu]

After:

2023-04-02  Eli Zaretskii  <eliz@gnu.org>

        * lisp/subr.el (use-dialog-box-p): Fix conditions for GUI dialogs.

dialog boxes will no longer be used when there is no last input event at
all, i.e. when `last-nonmenu-event' is nil.

Previously, `use-dialog-box-p' would only return nil if
`last-nonmenu-event' was a key event, which is the correct behavior;
`Fyes_or_no_p' still uses the correct test.

Why was that change made?