[clang] [static analyzer] Fix crash on parenthesized expression in assume attribute (PR #151682)

[Balazs Benics via cfe-commits]

https://github.com/steakhal requested changes to this pull request.

Hey, thank you for the patch. It looks like it was an easy fix!
I left a couple of minor remarks inline to address before we could merge this.
Thanks again!

https://github.com/llvm/llvm-project/pull/151682