Immediately return instead of setting bestValue

[FauziAkram]

Immediately return instead of setting bestValue, introducing a more aggressive use of the transposition table for early cutoffs.

Passed STC:
LLR: 2.95 (-2.94,2.94) <0.00,2.00>
Total: 12800 W: 3549 L: 3261 D: 5990
Ptnml(0-2): 48, 1398, 3241, 1644, 69
https://tests.stockfishchess.org/tests/view/679fa9f30774dfd78deb119b

Passed LTC:
LLR: 2.96 (-2.94,2.94) <0.50,2.50>
Total: 59106 W: 15483 L: 15112 D: 28511
Ptnml(0-2): 58, 6451, 16169, 6812, 63
https://tests.stockfishchess.org/tests/view/679fabd70774dfd78deb11a5

bench: 2484034

[xu-shawn]

The Elo trend from STC to LTC looks concerning, and indeed, reverting this change passes VVLTC:
LLR: 2.94 (-2.94,2.94) <0.50,2.50>
Total: 127786 W: 33173 L: 32713 D: 61900
Ptnml(0-2): 15, 11686, 40038, 12132, 22
https://tests.stockfishchess.org/tests/view/679fc8430774dfd78deb1285

[FauziAkram]

Yes indeed, I would have ran the VLTC myself, but you saved me some time, thanks Shawn <3