[DebugInfo] Do not assert on an unmarked end of a span

[kripken]

#8862 added binary tracking of Try, but it does not always fully work:
sometimes we note the start of a Try (this happens when we see a
Catch/CatchAll, and end the scope of the Try body), but we never
mark the end, because push() is not called on the Try in
wasm-ir-builder.cpp.

I could not quite figure out why push() is not called, and neither
could AI. It might be good to investigate this further, I left a
TODO, however, if we are dropping a little bit of debug info on
Try instructions then that is likely not a big deal, and also we were
doing it before #8862 anyhow.

Works around #8940

[tlively]

Can you share a reproducer? I'd be happy to look into what is going wrong in IRBuilder.

[kripken]

Sure, there is a reproducer in the linked issue that this works around, #8940

[kripken]

Btw, maybe our code is too complex if neither I nor AI could figure this out in a few hours? 😄