[clang] [analyzer] Fix crash of StreamChecker when eval calling 'fopen' (PR #100990)

[Balazs Benics via cfe-commits]

steakhal wrote:

I decided to put the fixup NFC changes along with this PR (the ones were submitted after I merged the original commit), but on hindsight probably it would be better to merge those NFC changes separately.
If you request, I'll split the PR.

https://github.com/llvm/llvm-project/pull/100990