[builtin-terminal-ui] Crash when typing in the middle of a prompt command that has completion

[lenormf]

Steps

No reproducer.

I was typing in the middle of a prompt command which had completion enabled, e.g.

:foo %(inserting text here) abc

The command is user-defined, and has a -shell-script-candidates scope assigned to handle completion candidates.

Outcome/Stacktrace

assert failed "start <= m_cursor_pos" at input_handler.cc:537
[Debug Infos]
pid: 1891548
callstack:
kak(Kakoune::Backtrace::Backtrace()+0x2b) [0x55de3e4991cf]
kak(Kakoune::on_assert_failed(char const*)+0x33) [0x55de3e498719]
kak(Kakoune::InputModes::LineEditor::insert_from(Kakoune::CharCount, Kakoune::StringView)+0x73) [0x55de3e626587]
kak(Kakoune::InputModes::Prompt::on_key(Kakoune::Key)+0x1170) [0x55de3e62a48a]
kak(Kakoune::InputMode::handle_key(Kakoune::Key)+0x51) [0x55de3e6224b7]
kak(+0x62029f) [0x55de3e62029f]
kak(Kakoune::InputHandler::handle_key(Kakoune::Key)+0x205) [0x55de3e6204a7]
kak(Kakoune::Client::process_pending_inputs()+0x363) [0x55de3e4cc4cb]
kak(Kakoune::ClientManager::process_pending_inputs()+0xc1) [0x55de3e4dcd85]
kak(Kakoune::run_server(Kakoune::StringView, Kakoune::StringView, Kakoune::StringView, Kakoune::Optional<Kakoune::BufferCoord>, Kakoune::ServerFlags, Kakoune::UIType, Kakoune::DebugFlags, Kakoune::ArrayView<Kakoune::StringView const>)+0xe2d) [0x55de3e684b5c]
kak(main+0x2690) [0x55de3e6890f6]
/usr/lib/libc.so.6(__libc_start_main+0xf2) [0x7f78455ca002]
kak(_start+0x2e) [0x55de3e49394e]