Fix indexing in comments

Author: sjvanrossum

sdks/java/io/kafka/src/main/java/org/apache/beam/sdk/io/kafka/KafkaUnboundedReader.java

@@ -151,8 +151,8 @@ public boolean start() throws IOException {
   @Override
   public boolean advance() throws IOException {
     /* Read first record (if any). we need to loop here because :
-     *  - (b) if curBatch is empty, we want to fetch next batch and then advance.
-     *  - (c) curBatch is an iterator of iterators. we interleave the records from each.
+     *  - (a) if curBatch is empty, we want to fetch next batch and then advance.
+     *  - (b) curBatch is an iterator of iterators. we interleave the records from each.
      *        curBatch.next() might return an empty iterator.
      */
     while (true) {
@@ -162,7 +162,7 @@ public boolean advance() throws IOException {
 
         PartitionState<K, V> pState = curBatch.next();
 
-        if (!pState.recordIter.hasNext()) { // -- (c)
+        if (!pState.recordIter.hasNext()) { // -- (b)
           pState.recordIter = Collections.emptyIterator(); // drop ref
           curBatch.remove();
           continue;
@@ -217,7 +217,7 @@ public boolean advance() throws IOException {
 
         kafkaResults.flushBufferedMetrics();
         return true;
-      } else { // -- (b)
+      } else { // -- (a)
         kafkaResults = KafkaSinkMetrics.kafkaMetrics();
         nextBatch();
         kafkaResults.flushBufferedMetrics();