Mistake in a96f1208cc.
When markers are present, offset should be added to the height.
Earlier it was subtracted like so `v2d->tot.ymin -= MarkerMargin` and that worked
because ymin is assigned like so `v2d->tot.ymin = -height`.
Now that the marker margin is added to the height it needs to be additive.
Pull Request: https://projects.blender.org/blender/blender/pulls/119647
43e968dc78