Crashing can lead to leftover git index files, which block later operations

[stephenmcgruer]

Opening mostly to track this; we are unlikely to address it unless it becomes a common pain-point. From #35 (where disk space caused a crash in the middle of git operations):

A 2020-07-22T11:46:32.040061728Z to delete:
A 2020-07-22T11:46:32.040082902Z to update: 10350 10449 11668 1234 14993 18228 18830 20165 20187 20239 20329 20351 20411 2092 21628 21646 21660 21696 21821 21959 22292 22348 22379 22504 22521 22566 22852 22854 22964 23137 23149 23281 23295 23336 23347 23369 23431 23504 23516 23527 23528 23541 23561 23562 23593 23594 23599 23638 23652 23691 23729 23789 23796 23845 23848 23853 23901 24010 24114 24133 24149 24155 24196 24200 24202 24220 24235 24342 24345 24352 24374 24394 24459 24511 24518 24521 24535 24556 24560 24566 24568 24599 24600 24601 24603 24608
A 2020-07-22T11:46:32.040092531Z to create: 24617 24618 24619 24633 24634 24658 24660 24662 24680 3060 4089 4354 4504
A 2020-07-22T11:46:32.042688789Z fatal: Unable to create '/root/wpt/.git/worktrees/10350/index.lock': File exists.
A 2020-07-22T11:46:32.042714968Z 
A 2020-07-22T11:46:32.042744895Z Another git process seems to be running in this repository, e.g.
A 2020-07-22T11:46:32.042753066Z an editor opened by 'git commit'. Please make sure all processes
A 2020-07-22T11:46:32.042758463Z are terminated then try again. If it still fails, a git process
A 2020-07-22T11:46:32.042764044Z may have crashed in this repository earlier:
A 2020-07-22T11:46:32.042788287Z remove the file manually to continue.