bug#35240: (elisp manual) typo in image-size function's description

[Eli Zaretskii]

> From: Takesi Ayanokoji <ayanokoji.takesi@gmail.com>
> Date: Fri, 12 Apr 2019 11:08:59 +0900
> 
> Elisp manual(desiplay.texi) says
> 
> http://git.savannah.gnu.org/cgit/emacs.git/tree/doc/lispref/display.texi#n5912
> 
> — Function: image-size spec &optional pixels frame
> 
>  This function returns the size of an image as a pair (width . height).spec 
> is an image specification. pixels
>  non-nil means return sizes measured in pixels, otherwise return sizes 
> measured in the default
>  character size of frame (see Frame Font). frame is the frame on which the 
> image will be displayed.
>  frame null or omitted means use the selected frame (see Input Focus).
> 
> ,but I think 'null' was intended meaning 'nil'.

Thanks, fixed.