Tweak miscast summon numbers a bit more (theTower, #9197)

Some of these numbers were unintentionally high because of off-by-one
errors in counting loop iterations. Fix those and tweak a few others,
and change all the loops to use > 0 so confusion is less likely.

<theTower> 1-3 for spatials, 2-3 for aboms, 1-3 worldbinders, 1-2 common
           demons, 2 shadows, 2-4 giant mites, 1-2 fire vortices, 2-5
           random_mobile_monsters
Simplify?  Condense, anyway.