[analyzer] Stability improvement for IteratorModeling

Summary:
Some function path may lead to crash.
Fixed using local variable outside the scope  through a pointer.
Fixed minor misspellings.
Added regression test.

This patch covers a bug https://bugs.llvm.org/show_bug.cgi?id=41485

Reviewed By: baloghadamsoftware

Differential Revision: https://reviews.llvm.org/D78289