bug#57349: 29.0.50; pixel-scroll-precision-mode. error integer-or-marker-p nil

[Eli Zaretskii]

> From: Gerd Möllmann <gerd.moellmann@gmail.com>
> Date: Tue, 23 Aug 2022 08:12:54 +0200
> 
> emacs -Q
> M-x pixel-scroll-precision-mode RET
> 
> Move the mouse to the lower right corner of the Emacs frame.  On macOS,
> the mouse cursor changes shape to a double-arrow pointing 45 degrees in
> the direction of the upper-left and lower-right corner of the screen.
> 
> Scroll the mouse wheel.
> 
> This either prints messages like this
> 
> <nil> <wheel-up> is undefined
> <nil> <double-wheel-up> is undefined
> <nil> <triple-wheel-up> is undefined [45 times]
> <nil> <wheel-down> is undefined

It may surprise this, but why do you think this is a problem?  How is
it different from what happens if you do this, for example:

  C-M-<F10>

(assuming that sequence is not bound to some command)?

> or sometimes errors 'Wrong type argument: integer-or-marker-p, nil'.

This shouldn't happen, indeed.

> Not sure what to make of this.  Looks like posn-at-x-y returns a posn
> with a nil point?  Or maybe posn-point returns nil?

Either this should be fixed, or the code should be prepared for nil in
this case.