Merge remote-tracking branch 'upstream/master'
Fix potential deadlock spotted by Richard Vida.
Generate Qsearch checks only at depth 0

An old idea retested at SPRT(0, 3) with 60+0.05 TC:
LLR: 2.95 (-2.94,2.94) [0.00,3.00]
Total: 98872 W: 15549 L: 15123 D: 68200

This is a very small elo increase patch so it really
stresses the limits of fishtest.

bench: 8596156
Release existing FileMappings when changing the path (Windows).
Merge remote-tracking branch 'upstream/master'
Merge remote-tracking branch 'upstream/master' into syzygy1lp
Merge remote-tracking branch 'syz/master' into syzygy1lp