fixes issue #2863

Issue

When dragging the top resize handles (ne, nw, n) of an image upwards,
the image would incorrectly expand instead of shrinking.

How to Test

Paste an Image and drag top left (nw) or top right (ne) corner to resize image:

Old effect : Extend on dragging in to shrink

Fixed effect : Shrink on dragging 'ne'/'nw' in and extend on dragging 'ne'/'nw' out

What

To fix, replaced nh with (+ oh sy) in TeXmacs/progs/generic/format-geometry-edit.scm:

;; BEFORE
((ne) (uniform-scale (/ (+ ow sx) ow) (/ nh oh)))
((nw) (uniform-scale (/ nw ow) (/ nh oh)))
((n)  (when (> nh 0.1) (tree-set! t 2 (cm->str nh)) (refresh-window)))

;; AFTER
((ne) (uniform-scale (/ (+ ow sx) ow) (/ (+ oh sy) oh)))
((nw) (uniform-scale (/ nw ow) (/ (+ oh sy) oh)))
((n)  (when (> (+ oh sy) 0.1) (tree-set! t 2 (cm->str (+ oh sy))) (refresh-window)))

Because Y increases upwards, stretching an image UP via ne, nw, n results in a positive sy. Therefore, the new height is calculated as :
Current Height + Stretch Height → (oh + sy)