message: add test for Zero-Length datagrams
  Summary: easy
diff: @@ -3845,6 +3845,20 @@ TEST_F(QuicTransportImplTest, DatagramCallbackDatagramAvailable) {
  transport->driveReadCallbacks();
  }
  +TEST_F(QuicTransportImplTest, ZeroLengthDatagram) {
  + NiceMock<MockDatagramCallback> datagramCb;
  + transport->enableDatagram();
  + transport->setDatagramCallback(&datagramCb);
  + transport->addDatagram(folly::IOBuf::copyBuffer(""));
  + EXPECT_CALL(datagramCb, onDatagramsAvailable());
  + transport->driveReadCallbacks();
  + auto datagrams = transport->readDatagrams();
  + EXPECT_FALSE(datagrams.hasError());
  + EXPECT_EQ(datagrams->size(), 1);
  + EXPECT_TRUE(datagrams->front() != nullptr);
  + EXPECT_EQ(datagrams->front()->computeChainDataLength(), 0);
  +}
  +
  TEST_F(QuicTransportImplTest, Cmsgs) {
  transport->setServerConnectionId();
  folly::SocketOptionMap cmsgs;
  