Move star draw to before sun glow texture draw and before sun draw,
not currently essential but the logical order. Will be necessary if
a 'no far ground' option is added, to draw stars behind the sun.
At sunset:
Stars first appear slightly later, at the time the sun disappears over the horizon,
this fixes seeing dark stars in front of the sun horizon glow texture.
Stars reach full brightness slightly earlier at time 20000, not so excessively long
after sunset.
The above behaviour is also applied at sunrise, but of course, time-inverted.
