Describe the bug
Defining a non-existant multiblock in a multiblock type page will crash the game

To Reproduce
Steps to reproduce the behavior:
2. Create book page of type multiblock and add a non-existing multiblock name there
3. When ingame, open that book page. => Crash

Expected behavior

• The game outputting either an error on launch, if multiblock registration info is available at this time already (similar to the other parsing errors)
• The game not crashing when opening a faulty multiblock type page, but instead rendering nothing, or an error text

System (please complete the following information):

• Modonomicon Version: modonomicon-1.20.1-fabric-1.42.0
• OS: Windows
• Minecraft Version: 1.20.1

I can attach a crash log when I'm back at my dev env

Interestingly that is a divergence between fabric and forge - on forge it already behaves as desired, showing the error when opening the book as all other errors. Will investigate!

EDIT: oddly enough the crash reproduced once, but now it properly shows the error on open ...
I made a small change to how book building/preprendering works but not sure if that will fix the issue.

Please ping me here to reopen if it persists in the next version, I currently cannot repro it but as I also failed to repro it more than once before the change it means little