[clang] [clang][analyzer] Fix assertion failure in StdLibraryFunctionsChecker with non-integral ssize_t (PR #209655)

[Balázs Benics via cfe-commits]

https://github.com/steakhal approved this pull request.

This was an interesting crash. I think the fix is correct.
I was thinking if this is the right place for the fix but I think it is.  Thanks!

https://github.com/llvm/llvm-project/pull/209655