Correct InnoDB calls to progress report API:
- second argument of thd_progress_init() is number of stages, one stage is
  enough for the row merge
- third argument of thd_progress_report() is some value indicating threshold,
  for the row merge it is file->offset
- second argument of thd_progress_report() is some value indicating current
  state, for the row merge it is file->offset - num_runs.