[llvm] [NativePDB] Fix crash in llvm-pdbutil (PR #164871)

[Alexandre Ganea via llvm-commits]

aganea wrote:

I feel `LazyRandomTypeCollection::tryGetType()` shouldn't be asserting, since it is returning an `std::optional`. If you change the `assert(contains(Index))` by returning a `std::nullopt` instead, this fixes the crash. @hans This also fixes `--id-index`.

https://github.com/llvm/llvm-project/pull/164871