Score and Select Best Thread in same loop (#2125)

This is a non-functional simplification that combines vote counting and thread selecting in the same loop.

It is possible that the best thread would be updated more frequently than master, but I'm not sure it matters here. Perhaps "mostVotes" is a better name than "bestVote?"

STC (stopped early).
LLR: 0.70 (-2.94,2.94) [-3.00,1.00]
Total: 10714 W: 2329 L: 2311 D: 6074
http://tests.stockfishchess.org/tests/view/5ccc71470ebc5925cf03d244

No functional change.