"git submodule" did not correctly adjust core.worktree setting that
indicates whether/where a submodule repository has its associated
working tree across various state transitions, which has been
corrected.

* sb/submodule-core-worktree:
  submodule deinit: unset core.worktree
  submodule: ensure core.worktree is set after update
  submodule: unset core.worktree if no working tree is present