[analyzer] Fix a crash for dereferencing an empty llvm::Optional variable in...

[analyzer] Fix a crash for dereferencing an empty llvm::Optional variable in SMTConstraintManager.h.

The first crash reported in the bug report 44338.

Condition `!isSat.hasValue() || isNotSat.getValue()` here should be
`!isNotSat.hasValue() || isNotSat.getValue()`.
`getValue()` here crashed when we used the static analyzer to analyze
postgresql-12.0.

Patch By: OikawaKirie

Reviewed By: steakhal, martong

Differential Revision: https://reviews.llvm.org/D83660