Reset page and item count on RepositoryItemReader#close()

When closing the RepositoryItemReader, this commit now resets the
current item index and page index to be 0 so that it can be reused
imediately (instead of requiring the reader be step scoped for the reset
to occur).

BATCH-2365

spring-batch-infrastructure/src/main/java/org/springframework/batch/item/data/RepositoryItemReader.java

@@ -216,6 +216,11 @@ public class RepositoryItemReader<T> extends AbstractItemCountingItemStreamItemR
 
 	@Override
 	protected void doClose() throws Exception {
+		synchronized (lock) {
+			current = 0;
+			page = 0;
+			results = null;
+		}
 	}
 
 	private Sort convertToSort(Map<String, Sort.Direction> sorts) {