[llvm] [TBAA] Only clear TBAAStruct if field can be extracted. (PR #81285)

[Florian Hahn via llvm-commits]

fhahn wrote:

@dobbelaj-snps ping :) 

Regarding your comment about this being to strict at the moment, the follow-on patches (in particular https://github.com/llvm/llvm-project/pull/81313) should address that separately. 

https://github.com/llvm/llvm-project/pull/81285