Fix break in nested scope inside a switch case

[m910q]

Fix setting allHadReturns = false; when a break; appears in a nested scope.

I'm not very familiar with how the compiler works, so it's an attempt that I hope can save you some time.

AI used to identify and make a bad fix
Human used to improve fix and do some manuel testing.

Fixes #2479

This PR does not fix how break; seems to be treated differently than return; when it comes to unreachable code within a single switch case. Compile time known branches works differently for instance:
if (compTimeFalseValue) { return; } is ignored as a return, but a break; is seen as a possibility, as far as I can tell.

[bfiete]

Can you provide some test methods that fail with the current implementation but pass with this fix?