message: rng/mwc64: fix mistake in how we amortize rng value
  closes
diff: @@ -46,7 +46,8 @@ public:
  _value = MWC();
  _index = 0;
  }
  - auto v = ((uint64_t *)&_value)[_index];
  + // grab either the top or bottom 32-bits of the 64-bit _value
  + uint32_t v = ((uint32_t *)&_value)[_index];
  _index++;
  return v;
  }
  