I removed the hack three weeks ago.
It did not work, whenever I clicked on a book in the file manager, KOReader started loading and eventually stopped. (I checked with "adb logcat".) When I tapped on the top of the screen, it finished loading (re-rendered the font each time). The image was also created. It worked fine when the Poke 2 was loaded with a USB cable. I did not notice any differences with adb.
Now I only changed the picture name in "screenshoter.lua" in line 42 to "screenshot.png" without date. So I just take a screenshot at the beginning of each book and that is the new screensaver.
Code:
self.screenshot_fn_fmt = screenshots_dir .. "screenshot.png"
But thank you all for your help and work. It was an honor for me.