message: Fix bug: don't access character in string that does not exist.
diff: @@ -72,7 +72,8 @@ bool EditTextBuffer::LineEdit(const TextDocumentContentChangeEvent &c,
  std::string *str) {
  int end_char = c.range.end.character;
  - const int str_end = str->back() == '\n' ? str->length() - 1 : str->length();
  + const int str_end = (!str->empty() && str->back() == '\n') ? str->length() - 1
  + : str->length();
  if (c.range.start.character > str_end) return false;
  if (end_char > str_end) end_char = str_end;
  if (end_char < c.range.start.character) return false;
  