message: fix crash in memset_pattern with bytesize != 1
diff: @@ -1892,8 +1892,9 @@ void Memory::memset_pattern(const expr &ptr0, const expr &pattern0,
  }
  store(ptr, to_store, undef_vars, 1);
  } else {
  - for (unsigned i = 0; i < pattern_length; ++i) {
  - to_store.emplace_back(i * bytesz, std::move(bytes[i])());
  + assert(bytes.size() * bytesz == pattern_length);
  + for (unsigned i = 0; i < pattern_length; i += bytesz) {
  + to_store.emplace_back(i * bytesz, std::move(bytes[i/bytesz])());
  }
  expr offset
  = expr::mkFreshVar("#off", expr::mkUInt(0, Pointer::bitsShortOffset()));
  