Fix +M0 score when low on time

When time remaining is less than Emergency Move Time,
we won't even complete one iteration and engine reports
a stale +M0 score.

To reproduce run "go wtime 10"

info depth 1 seldepth 1 score mate 0 upperbound nodes 2 nps 500 time 4 multipv 1 pv a2a3
info nodes 2 time 4
bestmove a2a3 ponder (none)

This patch fixes the issue.

Tested by Binky at very short TC: 0.05+0.05
ELO: 5.96 +-12.9 (95%) LOS: 81.7%
Total: 1458 W: 394 L: 369 D: 695

And at a bit longer TC:
ELO: 1.56 +-3.7 (95%) LOS: 79.8%
Total: 16511 W: 3983 L: 3909 D: 8619

bench: 7804908