[clang-tidy] Fix PR26274

Summary:
This commit fixes http://llvm.org/PR26274 in a simpler and more correct way than
4736d63f did. See
https://reviews.llvm.org/D69855#1767089 for details.

Reviewers: gribozavr, aaron.ballman, gribozavr2

Reviewed By: aaron.ballman, gribozavr2

Subscribers: gribozavr2, merge_guards_bot, xazax.hun, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D70974