Fix commentary in dispnew.c

* src/dispnew.c (buffer_posn_from_coords): Fix inaccuracies in
the commentary.

src/dispnew.c

@@ -5097,13 +5097,15 @@ update_frame_line (struct frame *f, int vpos, bool updating_menu_p)
  ***********************************************************************/
 
 /* Determine what's under window-relative pixel position (*X, *Y).
-   Return the OBJECT (string or buffer) that's there.
+   Return the object (string or buffer) that's there.
    Return in *POS the position in that object.
    Adjust *X and *Y to character positions.
+   If an image is shown at the specified position, return
+   in *OBJECT its image-spec.
    Return in *DX and *DY the pixel coordinates of the click,
-   relative to the top left corner of OBJECT, or relative to
+   relative to the top left corner of object, or relative to
    the top left corner of the character glyph at (*X, *Y)
-   if OBJECT is nil.
+   if the object at (*X, *Y) is nil.
    Return WIDTH and HEIGHT of the object at (*X, *Y), or zero
    if the coordinates point to an empty area of the display.  */