Fix a sequential only build warning and a too restrictive Assert

src/utils/Messenger.cpp

@@ -28,7 +28,7 @@ Messenger::destroy()
   }
 }
 
-Messenger::Messenger([[maybe_unused]] int& argc, [[maybe_unused]] char* argv[], bool parallel_output)
+Messenger::Messenger([[maybe_unused]] int& argc, [[maybe_unused]] char* argv[], [[maybe_unused]] bool parallel_output)
 {
 #ifdef PUGS_HAS_MPI
   MPI_Init(&argc, &argv);

src/utils/ReproducibleSumUtils.hpp

@@ -168,7 +168,7 @@ class ReproducibleScalarSum
   PUGS_INLINE static void
   _update(const DataType& m, Bin& bin) noexcept(NO_ASSERT)
   {
-    Assert(m > 0);
+    Assert(m >= 0);
 
     using namespace reproducible_sum_utils;
     if (m >= std::pow(DataType{2}, W - 1.) * ulp(bin.S[0])) {