fix race in Replayer

java.lang.IllegalStateException: Unknown session: sessionId=1,connectionId=1862197465265022976
	at uk.co.real_logic.artio.engine.logger.Replayer.processResendRequest(Replayer.java:387)
	at uk.co.real_logic.artio.engine.logger.Replayer.onResendRequest(Replayer.java:315)
	at uk.co.real_logic.artio.engine.logger.Replayer.onFragment(Replayer.java:208)
	at io.aeron.Image.controlledPoll(Image.java:385)
	at io.aeron.Subscription.controlledPoll(Subscription.java:235)
	at uk.co.real_logic.artio.engine.logger.Replayer.doWork(Replayer.java:473)
	at org.agrona.concurrent.CompositeAgent.doWork(CompositeAgent.java:120)
	at org.agrona.concurrent.AgentRunner.doWork(AgentRunner.java:304)
	at org.agrona.concurrent.AgentRunner.workLoop(AgentRunner.java:296)
	at org.agrona.concurrent.AgentRunner.run(AgentRunner.java:162)
	at java.base/java.lang.Thread.run(Thread.java:840)

artio-core/src/main/java/uk/co/real_logic/artio/engine/logger/Replayer.java

@@ -384,7 +384,9 @@ else if (fixPConnectionIds.contains(connectionId))
             return session;
         }
 
-        throw new IllegalStateException("Unknown session: sessionId=" + sessionId + ",connectionId=" + connectionId);
+        // ManageSession and ValidResendRequest might race each other (different sessions), so it's possible we see
+        // VRR before MS and sessionCodecs is null, simply wait in this case for the other image to catch up.
+        return null;
     }
 
     private FixReplayerSession processFixResendRequest(