message: meshable_arena: fix NDEBUG logic
diff: @@ -252,7 +252,7 @@ internal::RelaxedBitmap MeshableArena::allocatedBitmap(bool includeDirty) const
  auto unmarkPages = [&](const Span &span) {
  for (size_t k = 0; k < span.length; k++) {
  -#ifdef NDEBUG
  +#ifndef NDEBUG
  if (!bitmap.isSet(span.offset + k)) {
  debug("arena: bit %zu already unset 1 (%zu/%zu)\n", k, span.offset, span.length);
  }
  