BATCH-2151: Clean up ChunkMonitor offset on chunk boundries

spring-batch-core/src/main/java/org/springframework/batch/core/step/item/ChunkMonitor.java

@@ -140,6 +140,7 @@ public class ChunkMonitor extends ItemStreamSupport {
 				// Only call the underlying update method if we are on a chunk
 				// boundary
 				stream.update(executionContext);
+				executionContext.remove(getExecutionContextKey(OFFSET));
 			}
 			else {
 				executionContext.putInt(getExecutionContextKey(OFFSET), data.offset);

spring-batch-core/src/test/java/org/springframework/batch/core/step/item/ChunkMonitorTests.java

@@ -128,6 +128,10 @@ public class ChunkMonitorTests {
 		ExecutionContext executionContext = new ExecutionContext();
 		monitor.update(executionContext);
 		assertEquals(0, executionContext.size());
+
+		executionContext.put(ChunkMonitor.class.getName() + ".OFFSET", 3);
+		monitor.update(executionContext);
+		assertEquals(0, executionContext.size());
 	}
 
 	@Test