sn parallel on non-existent paths creates an infinite loop

[hcpl]

For example, create an empty directory and call sn p foo in it.

[hcpl]

The culprit is this section:

tin-summer/src/walk_parallel/mod.rs

Lines 375 to 386 in 81e2db0

	// assign work to everyone
	Walk::push_subdir(&w, &mut worker, &arc_local);
	// start popping off values in the worker's thread
	loop {
	if let Pop::Data(p) = worker.pop() {
	match p {
	Status::Data(d) => Walk::print_dir(&d, &arc_local),
	_ => break,
	}
	}
	}

If the path doesn't exist then Walk::push_subdir doesn't assign any work to the worker. So in turn, worker.pop() will always return Pop::Empty and the loop silently ignores this case, creating an infinite loop.