Update the rows read counter after processing the scan range instead of updating
it after reading every row for sequence files to save CPU cycles.
Change-Id: Ie42c97a36e46172884cc497aa645036c2c11f541
Reviewed-on: http://gerrit.cloudera.org:8080/6522
Reviewed-by: Bharath Vissapragada <bharathv@cloudera.com>
Tested-by: Impala Public Jenkins