Rendering of the rinohtype manuals stalls at specific pages

[brechtm]

• [ ] determine the cause
• [ ] investigate whether this can be sped up

[brechtm]

Actually, rendering doesn't stall but I think the page numbers/time in the progress indicator are not being updated when rendering a long flowable that spans multiple pages. Only the first page number is shown in the progress indicator and subsequent page numbers are skipped.