[clang] [Sema] LambdaScopeForCallOperatorInstantiationRAII - fix typo in early out logic (PR #96888)

[Simon Pilgrim via cfe-commits]

RKSimon wrote:

Cheers - I'll push this (without the assert) in a moment - that shouldn't get in the way of working out why they aren't always paired.

https://github.com/llvm/llvm-project/pull/96888