Race between creating ProgressRecorder and setting its progress

If a ProgressRecorder is created, its state is not initialized until set_progress() is called. During this time, I think there is a race condition where a page calling initProgressBar() can get a bad state === null and fall into onTaskError() during this time.
(progressBarMessageElement will say "Uh-Oh, something went wrong! Unknown state")

Trace the ProgressRecorder creation and set_progress() path alongside the initProgressBar() and onTaskError() entry points. Check the interval between creation and progress initialization, then verify that initProgressBar() no longer receives state === null or reports "Unknown state" during that interval.

Written by the indexing model from the issue text.