Panic when using help menu

Describe the bug

When using completions from the help menu, certain behaviours cause a panic in reedline:

1. If the line is non-empty and the help menu is used to find a command, typing any non-return character causes a panic
2. If the line is empty and the help menu is used to find a command, typing the space character causes a panic.

How to reproduce

1. Type some string into the command prompt
2. Open the help menu (using some keybind)
3. Type a search term and select a suggestion
4. Type a non-return character

Expected behavior

I expect nu to not panic. Furthermore, I expect nu to parse the command and behave as it would if the help command was not used and the "helped command" was inputted manually.

Screenshots

No response

Configuration

Additional context

Here is the backtrace:

/u5/dsnelgro/nushell〉hlsthread 'main' panicked at 'assertion failed: self.is_char_boundary(idx)', /rustc/4b91a6ea7258a947e59c6522cd5898e7c0a6a88f/library/alloc/src/string.rs:1530:9
stack backtrace:
   0: rust_begin_unwind
             at /rustc/4b91a6ea7258a947e59c6522cd5898e7c0a6a88f/library/std/src/panicking.rs:584:5
   1: core::panicking::panic_fmt
             at /rustc/4b91a6ea7258a947e59c6522cd5898e7c0a6a88f/library/core/src/panicking.rs:142:14
   2: core::panicking::panic
             at /rustc/4b91a6ea7258a947e59c6522cd5898e7c0a6a88f/library/core/src/panicking.rs:48:5
   3: alloc::string::String::insert
             at /rustc/4b91a6ea7258a947e59c6522cd5898e7c0a6a88f/library/alloc/src/string.rs:1530:9
   4: reedline::core_editor::line_buffer::LineBuffer::insert_char
             at /u5/dsnelgrove/.cargo/git/checkouts/reedline-e42026a78d91c510/f949f56/src/core_editor/line_buffer.rs:342:9
   5: reedline::core_editor::editor::Editor::run_edit_command
             at /u5/dsnelgrove/.cargo/git/checkouts/reedline-e42026a78d91c510/f949f56/src/core_editor/editor.rs:57:43
   6: reedline::engine::Reedline::run_edit_commands
             at /u5/dsnelgrove/.cargo/git/checkouts/reedline-e42026a78d91c510/f949f56/src/engine.rs:1173:13
   7: reedline::engine::Reedline::handle_editor_event
             at /u5/dsnelgrove/.cargo/git/checkouts/reedline-e42026a78d91c510/f949f56/src/engine.rs:915:17
   8: reedline::engine::Reedline::handle_event
             at /u5/dsnelgrove/.cargo/git/checkouts/reedline-e42026a78d91c510/f949f56/src/engine.rs:586:13
   9: reedline::engine::Reedline::read_line_helper
             at /u5/dsnelgrove/.cargo/git/checkouts/reedline-e42026a78d91c510/f949f56/src/engine.rs:563:23
  10: reedline::engine::Reedline::read_line
             at /u5/dsnelgrove/.cargo/git/checkouts/reedline-e42026a78d91c510/f949f56/src/engine.rs:440:22
  11: nu_cli::repl::evaluate_repl
             at ./crates/nu-cli/src/repl.rs:340:21
             at ./src/main.rs:458:31
  13: core::ops::function::FnOnce::call_once
             at /rustc/4b91a6ea7258a947e59c6522cd5898e7c0a6a88f/library/core/src/ops/function.rs:248:5
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

Reproduce the help-menu interaction described in the issue, then start with reedline's core_editor/line_buffer.rs at LineBuffer::insert_char and core_editor/editor.rs at Editor::run_edit_command, as identified by the backtrace. Trace how selecting a help suggestion changes the line and verify that subsequent non-return input does not panic and preserves the expected command behavior.