[clang-tools-extra] [NFC] Fix uninitialized scalar field in constructor. (PR #118324)

[Nathan Ridge via cfe-commits]

HighCommander4 wrote:

Seems like `MemIndex::IdxContents` has the same issue.

It's a bit suspicious to me that the other `DexIndex` and `MemIndex` constructors are not passing in a `IndexContents` value. Either there's a bug lurking there, or the field is only relevant in certain situations (e.g. only for dynamic indexes) in which case that should be documented at the field's declaration. Would you mind filing a follow-up issue about auditing this situation more carefully, so it doesn't get forgotten?

https://github.com/llvm/llvm-project/pull/118324