[LLDB][NativePDB] Fix name access for classes in `CVTagRecord::name` (#151190)
From
https://github.com/llvm/llvm-project/pull/149876#discussion_r2240478480:
The `name()` accessor checked for `m_kind == Union` and accessed
`cvclass` instead of `cvunion`. This is technically wrong (maybe UB
even?).
In practice, this wasn't an issue, because all types in the union
(`ClassRecord`/`EnumRecord`/`UnionRecord`) inherit from `TagRecord`.