optimize the smart text reflow

[mengwong]

at present it adds 20+ pages to the end of everything, which makes the process super slow. figure out why exactly smart text reflow isn't working.

maybe we can trap the "Invalid Object for this request" error and only append pages if that error occurs, then try again.

maybe we need to test if the last page of the template is threaded to a previous page, and if it isn't, create that by hand, to encourage smart text reflow to operate.