]NFC][Clang] Fix Coverity bug with dereference null return value in clang::​CodeGen::​CodeGenFunction::​EmitOMPArraySectionExpr()

[Manna]

Summary

Reported by Coverity:

Inside "CGExpr.cpp" file, in clang::​CodeGen::​CodeGenFunction::​EmitOMPArraySectionExpr(clang::​OMPArraySectionExpr const *, bool): Return value of function which returns null is dereferenced without checking.

  } else {
	//returned_null: getAsConstantArrayType returns nullptr (checked 83 out of 95 times).
	// var_assigned: Assigning: CAT = nullptr return value from getAsConstantArrayType.
    auto *CAT = C.getAsConstantArrayType(ArrayTy);
	//identity_transfer: Member function call CAT->getSize() returns an offset off CAT (this). 
	
   // Dereference null return value (NULL_RETURNS)
   //dereference: Dereferencing a pointer that might be nullptr CAT->getSize() when calling APInt. 
   ConstLength = CAT->getSize();
  }

This patch adds an assert to resolve the bug.

[Manna]

Thank you @erichkeane for reviews!

clang/lib/CodeGen/CGExpr.cpp

if (Length) {
       if (auto *VAT = C.getAsVariableArrayType(ArrayTy)) {
         Length = VAT->getSizeExpr();
         if (std::optional<llvm::APSInt> L = Length->getIntegerConstantExpr(C)) {
           ConstLength = *L;
           Length = nullptr;
         }
       } else {
         auto *CAT = C.getAsConstantArrayType(ArrayTy);
+        assert(CAT && "unexpected type for array initializer");
         ConstLength = CAT->getSize();
       }
       if (Length) {
         auto *LengthVal = Builder.CreateIntCast(
             EmitScalarExpr(Length), IntPtrTy,
             Length->getType()->hasSignedIntegerRepresentation());
         Idx = Builder.CreateSub(
             LengthVal, llvm::ConstantInt::get(IntPtrTy, /*V=*/1), "len_sub_1",