[clang] [clang][Sema] fix crash on invalid expression with trailing return type and template keyword (PR #191972)

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firstmoonlight wrote:

> Were LLMs used in this PR?
I use it primarily for generating git commit messages and, when reading code, for analyzing code logic and understanding class members. Although the information it provides is often incomplete or incorrect, it is still very helpful overall.


https://github.com/llvm/llvm-project/pull/191972