message: Release DurationStr if need (lib)
diff: @@ -604,6 +604,10 @@ TogglTimelineEventView *timeline_event_view_init(
  void timeline_event_view_update_duration(TogglTimelineEventView *event_view, const int64_t duration) {
  event_view->Duration = duration;
  + if (event_view->DurationString) {
  + free(event_view->DurationString);
  + event_view->DurationString = nullptr;
  + }
  event_view->DurationString = copy_string(toggl::Formatter::FormatDuration(duration, toggl::Format::ImprovedOnlyMinAndSec));
  }
  