Crash when formatting document 2

[getreu]

Steps to reproduce

1. Create a file tmp.md with the following content

   word word word
   word word word
   word word word
   

2. Select all with %

3. Pipe all with | through fmt

Backtrace

$ RUST_BACKTRACE=1 hx tmp.md
thread 'main' panicked at 'called Result::unwrap() on an Err value: Char index out of bounds: char index 59, Rope/RopeSlice char length 30', /home/getreu/.cargo/registry/src/git.luolix.top-1ecc6299db9ec823/ropey-1.5.0/src/slice.rs:349:41
stack backtrace:

   0: rust_begin_unwind
             at /rustc/fe5b13d681f25ee6474be29d748c65adcd91f69e/library/std/src/panicking.rs:584:5
   1: core::panicking::panic_fmt
             at /rustc/fe5b13d681f25ee6474be29d748c65adcd91f69e/library/core/src/panicking.rs:143:14
   2: core::result::unwrap_failed
             at /rustc/fe5b13d681f25ee6474be29d748c65adcd91f69e/library/core/src/result.rs:1785:5
   3: ropey::slice::RopeSlice::char_to_byte
   4: helix_core::graphemes::nth_next_grapheme_boundary
   5: helix_core::selection::Range::grapheme_aligned
   6: helix_core::selection::Selection::ensure_invariants
   7: helix_view::document::Document::apply_impl
   8: helix_view::document::Document::apply
   9: helix_term::commands::shell
  10: <helix_term::ui::prompt::Prompt as helix_term::compositor::Component>::handle_event
  11: helix_term::compositor::Compositor::handle_event
  12: helix_term::application::Application::handle_terminal_events
  13: hx::main_impl::{{closure}}
  14: std::thread::local::LocalKey<T>::with
  15: tokio::park::thread::CachedParkThread::block_on
  16: tokio::runtime::scheduler::multi_thread::MultiThread::block_on
  17: tokio::runtime::Runtime::block_on
  18: hx::main
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

[getreu]

Similar, but different: #4673

[archseer]

Feels wrong that shell is manually calculating the selection ranges:

helix/helix-term/src/commands.rs

Lines 4776 to 4803 in fd585c1

	for range in selection.ranges() {
	let fragment = range.slice(text);
	let (output, success) = match shell_impl(shell, cmd, pipe.then(|| fragment.into())) {
	Ok(result) => result,
	Err(err) => {
	cx.editor.set_error(err.to_string());
	return;
	}
	};
	if !success {
	cx.editor.set_error("Command failed");
	return;
	}
	let (from, to) = match behavior {
	ShellBehavior::Replace => (range.from(), range.to()),
	ShellBehavior::Insert => (range.from(), range.from()),
	ShellBehavior::Append => (range.to(), range.to()),
	_ => (range.from(), range.from()),
	};
	ranges.push(Range::new(to, to + output.chars().count()));
	changes.push((from, to, Some(output)));
	}
	if behavior != &ShellBehavior::Ignore {
	let transaction = Transaction::change(doc.text(), changes.into_iter())
	.with_selection(Selection::new(ranges, selection.primary_index()));

Maybe all that should just be stripped out