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

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.

Differential Revision: https://reviews.llvm.org/D106693