[flang] Fix IsSimplyContiguous() for the case of a pointer component

[klausler]

Summary

The result expression for the analysis of a Component is not (longer)
valid in the expression traversal framework used by IsSimplyContiguousHelper
now that it has a tri-state result. Fix so that any result of
analyzing the component symbol is required to be true, not just
present.

flang/lib/Evaluate/check-expression.cpp

if (ultimate.attrs().test(semantics::Attr::CONTIGUOUS) ||
       return assoc;
     } else {
       return false;
     }
   }
 
   Result operator()(const ArrayRef &x) const {
     const auto &symbol{x.GetLastSymbol()};
-    if (!(*this)(symbol)) {
+    if (!(*this)(symbol).has_value()) {
       return false;
     } else if (auto rank{CheckSubscripts(x.subscript())}) {
       // a(:)%b(1,1) is not contiguous; a(1)%b(:,:) is
       return *rank > 0 || x.Rank() == 0;
     } else {
       return false;
     }
   }
   Result operator()(const CoarrayRef &x) const {
     return CheckSubscripts(x.subscript()).has_value();
   }
   Result operator()(const Component &x) const {
-    return x.base().Rank() == 0 && (*this)(x.GetLastSymbol());
+    return x.base().Rank() == 0 && (*this)(x.GetLastSymbol()).value_or(false);
   }
   Result operator()(const ComplexPart &) const { return false; }
   Result operator()(const Substring &) const { return false; }
 
   template <typename T> Result operator()(const FunctionRef<T> &x) const {
     if (auto chars{
             characteristics::Procedure::Characterize(x.proc(), context_)}) {
       if (chars->functionResult) {