ReduceOps: reset result readiness flag

In AMReX-Codes#3421, a change was made to avoid a common mistake of calling
ReduceData::value multiple times. Unfortunately, it breaks codes that using
one ReduceOps with multiple ReduceData objects. This PR fixes both cases.

Src/Base/AMReX_Reduce.H

@@ -258,6 +258,7 @@ public:
  * m_max_blocks * sizeof(Type)))),
  m_fn_value([&reduce_op,this] () -> Type { return this->value(reduce_op); })
  {
+ reduce_op.m_result_is_ready = false;
  static_assert(std::is_trivially_copyable<Type>(),
  "ReduceData::Type must be trivially copyable");
  static_assert(std::is_trivially_destructible<Type>(),
@@ -993,6 +994,7 @@ public:
  : m_tuple(OpenMP::in_parallel() ? 1 : OpenMP::get_max_threads()),
  m_fn_value([&reduce_op,this] () -> Type { return this->value(reduce_op); })
  {
+ reduce_op.m_result_is_ready = false;
  for (auto& t : m_tuple) {
  Reduce::detail::for_each_init<0, Type, Ps...>(t);
  }