[analyzer] Fix crash in RangedConstraintManager.cpp

This change fixes a crash in RangedConstraintManager.cpp:assumeSym due to an
unhandled BO_Div case.

clang: <root>clang/lib/StaticAnalyzer/Core/RangedConstraintManager.cpp:51:
  virtual clang::ento::ProgramStateRef
  clang::ento::RangedConstraintManager::assumeSym(clang::ento::ProgramStateRef,
    clang::ento::SymbolRef, bool):
  Assertion `BinaryOperator::isComparisonOp(Op)' failed.

Reviewed By: NoQ

Differential Revision: https://reviews.llvm.org/D122277