[clang] [Clang][Sema] Fix crash in UnresolvedMemberExpr check (PR #209792)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

This seems reasonable to me, but I don't have a great hold on this, hoping the others can take a closer look.

https://github.com/llvm/llvm-project/pull/209792