Merge branch 'nd/worktree-list-fixup' into maint

The output from "git worktree list" was made in readdir() order, and was unstable. * nd/worktree-list-fixup: worktree list: keep the list sorted worktree.c: get_worktrees() takes a new flag argument get_worktrees() must return main worktree as first item even on error worktree: reorder an if statement worktree.c: zero new 'struct worktree' on allocation