Fix tui-prompts test failures

[joshka]

---- text_prompt::tests::draw_no_wrap stdout ----
thread 'text_prompt::tests::draw_no_wrap' panicked at src/text_prompt.rs:383:9:
assertion `left == right` failed
  left: (16, 1)
 right: (16, 0)
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

---- text_prompt::tests::draw_wrapped stdout ----
thread 'text_prompt::tests::draw_wrapped' panicked at src/text_prompt.rs:440:9:
assertion `left == right` failed
  left: (16, 1)
 right: (5, 1)


failures:
    text_prompt::tests::draw_no_wrap
    text_prompt::tests::draw_wrapped

[joshka]

(Search FIXME) for these (I've made them document existing behavior instead of failing for now)