[Chapter 40] Stealth fix for chapter 33 is not mentioned in the course

https://github.com/amethyst/rustrogueliketutorial/blob/33872fe582f226178436847e1f74eafcbf9c0d1a/chapter-40-doors/src/map_builders/waveform_collapse/mod.rs#L40-L41

In chapter 40, there is an update to the code of `WaveformCollapseBuilder` (introduced in chapter 33).
It adds a try limit to the solver loop to avoid an infinite (or at least a very long) loop.
(Not sure, but I think the additional lines to clear `spawn_list`, `rooms`, and `corridors` after making a copy of the map are also part of the fix).

However, this is not mentioned anywhere in the chapter (or in the book), so people will have to power through the following chapters with a level generation that breaks regularly.