[flang] Only apply PointerIsAssociatedWith fix for derived-type

[clementval]

Summary

Only apply the change made in D145604 for derived-type.
zero-sized character for example are supposed to give a false result

[PeteSteinfeld]

All builds and tests correctly and looks good.

flang/runtime/pointer.cpp

bool RTNAME(PointerIsAssociated)(const Descriptor &pointer) {
   return pointer.raw().base_addr != nullptr;
 }
 
 bool RTNAME(PointerIsAssociatedWith)(
     const Descriptor &pointer, const Descriptor *target) {
   if (!target) {
     return pointer.raw().base_addr != nullptr;
   }
-  if (!target->raw().base_addr) {
+  if (!target->raw().base_addr ||
+      (target->raw().type != CFI_type_struct && target->ElementBytes() == 0)) {
     return false;
   }
   int rank{pointer.rank()};
   if (pointer.raw().base_addr != target->raw().base_addr ||
       pointer.ElementBytes() != target->ElementBytes() ||
       rank != target->rank()) {
     return false;
   }