message: Fix flexbuffers clang-analyzer warning
diff: @@ -851,6 +851,7 @@ inline Reference Map::operator[](const char *key) const {
  case 2: comp = KeyCompare<uint16_t>; break;
  case 4: comp = KeyCompare<uint32_t>; break;
  case 8: comp = KeyCompare<uint64_t>; break;
  + default: FLATBUFFERS_ASSERT(false); return Reference();
  }
  auto res = std::bsearch(key, keys.data_, keys.size(), keys.byte_width_, comp);
  if (!res) return Reference(nullptr, 1, NullPackedType());
  