Undo redo panic

[CptPotato]

Helix sometimes produces a panic after using undo redo.

minimal reproduction:

1. open helix
2. enter i a Esc u :later o

Interestingly, when using :earlier instead of u the panic does not occur.

---

backtrace

thread 'main' panicked at 'assertion failed: self.len_after == other.len', helix-core\src\transaction.rs:128:9
stack backtrace:
   0: std::panicking::begin_panic_handler
             at /rustc/59eed8a2aac0230a8b53e89d4e99d55912ba6b35\/library\std\src\panicking.rs:517
   1: core::panicking::panic_fmt
             at /rustc/59eed8a2aac0230a8b53e89d4e99d55912ba6b35\/library\core\src\panicking.rs:101
   2: core::panicking::panic
             at /rustc/59eed8a2aac0230a8b53e89d4e99d55912ba6b35\/library\core\src\panicking.rs:50
   3: helix_core::transaction::ChangeSet::compose
   4: helix_view::document::Document::apply
   5: helix_term::commands::append_to_line
   6: helix_term::ui::editor::EditorView::render_statusline
   7: <helix_term::ui::editor::EditorView as helix_term::compositor::Component>::handle_event
   8: helix_term::application::Application::handle_terminal_events
   9: <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll
  10: tokio::park::thread::CachedParkThread::block_on
  11: tokio::runtime::thread_pool::ThreadPool::block_on
  12: tokio::runtime::Runtime::block_on
  13: hx::setup_logging