ApplyThenWaitUntilApplied supplies wrong epoch for executeAtEpoch

Patch by Ariel Weisberg; Reviewed by Benedict Elliott Smith for CASSANDRA-19687

modules/accord

@@ -1 +1 @@
-Subproject commit 527094c69ad23319b058917b1c8974d01c5d86e6
+Subproject commit 37c957c719491634f081b39900ebf708079ef3ee

src/java/org/apache/cassandra/index/accord/CheckpointIntervalArrayIndex.java

@@ -615,6 +615,8 @@ public class CheckpointIntervalArrayIndex
                 }, (i1, i2, i3, i4, startIdx, endIdx) -> {
                     try
                     {
+                        if (startIdx == endIdx)
+                            return;
                         reader.maybeSeek(indexInput, stats, SortedListReader.SeekReason.SCAN, reader.fileOffsetStart(startIdx));
                         for (int i = startIdx; i < endIdx; i++)
                         {

src/java/org/apache/cassandra/service/accord/serializers/ReadDataSerializers.java

@@ -81,7 +81,6 @@ public class ReadDataSerializers
         {
             CommandSerializers.txnId.serialize(msg.txnId, out, version);
             KeySerializers.participants.serialize(msg.readScope, out, version);
-            out.writeUnsignedVInt(msg.executeAtEpoch);
             CommandSerializers.timestamp.serialize(msg.executeAt, out, version);
             KeySerializers.fullRoute.serialize(msg.route, out, version);
             CommandSerializers.partialTxn.serialize(msg.txn, out, version);
@@ -97,7 +96,6 @@ public class ReadDataSerializers
             return ApplyThenWaitUntilApplied.SerializerSupport.create(
             CommandSerializers.txnId.deserialize(in, version),
             KeySerializers.participants.deserialize(in, version),
-            in.readUnsignedVInt(),
             CommandSerializers.timestamp.deserialize(in, version),
             KeySerializers.fullRoute.deserialize(in, version),
             CommandSerializers.partialTxn.deserialize(in, version),
@@ -112,7 +110,6 @@ public class ReadDataSerializers
         {
             return CommandSerializers.txnId.serializedSize(msg.txnId, version)
                    + KeySerializers.participants.serializedSize(msg.readScope, version)
-                   + TypeSizes.sizeofUnsignedVInt(msg.executeAtEpoch)
                    + CommandSerializers.timestamp.serializedSize(msg.executeAt, version)
                    + KeySerializers.fullRoute.serializedSize(msg.route, version)
                    + CommandSerializers.partialTxn.serializedSize(msg.txn, version)