message: fix assertion failure when storing invalid data
diff: @@ -45,7 +45,7 @@ public:
  expr byteofs = expr::mkUInt(i, 3);
  expr np = non_poison.toBVBool();
  p = expr::mkUInt(1, 1).concat(np).concat(ptr()).concat(byteofs);
  - assert(p.bits() == m.bitsByte());
  + assert(!p.isValid() || p.bits() == m.bitsByte());
  }
  // Creates a non-pointer byte that has data and non_poison.
  