Move storm special condition to UnblockedStorm array (#2210)

This is a functional simplification.

Looks like we can accommodate the special initialization of Value in evaluate_shelter in the UnblockedStorm array.

STC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 32483 W: 7422 L: 7322 D: 17739
http://tests.stockfishchess.org/tests/view/5d14c5f80ebc5925cf0b48da

LTC
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 35361 W: 6139 L: 6042 D: 23180
http://tests.stockfishchess.org/tests/view/5d14d69c0ebc5925cf0b4bd0

Bench 3596270