message: Take into account backtracking at the prompt
diff: @@ -113,10 +113,11 @@ impl<'a, 'b> Completer for IonCompleter<'a, 'b> {
  if let EventKind::BeforeComplete = event.kind {
  let (words, pos) = event.editor.get_words_and_cursor_position();
  - self.completion = match (words.len(), pos) {
  - (0, _) => CompletionType::Nothing,
  - (1, CursorPosition::InSpace(..)) => CompletionType::VariableAndFiles,
  - (1, _) => CompletionType::Command,
  + self.completion = match pos {
  + _ if words.is_empty() => CompletionType::Nothing,
  + CursorPosition::InWord(0) | CursorPosition::OnWordRightEdge(0) => {
  + CompletionType::Command
  + }
  _ => CompletionType::VariableAndFiles,
  };
  }
  