When using the interactive add tool for primitives with a fixed
height and base aspect ratio, the height of the created primitive
would be incorrect (two times too small or two times too big).

When the base origin was centered, the fixed_aspect_dimension
was not changed even though the base length was doubled.
Additionally, when the height origin was centered but the height
aspect ration was fixed, the height was doubled leading to an
incorrect size.

The fix doubles fixed_aspect_dimension when the base origin is
centered and correctly calculates the height of the primitive when
the aspect ration is set to fixed.