Fix a few bugs in the AnalyticEvalNode

IMPALA-1233: Crash running query with analytic in WITH clause
IMPALA-1232: Analytic eval node crashes if cancelling query before Open()

Change-Id: I9a263775b8ef670d0f819ed53d0af1eb96edf5c7
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/4313
Reviewed-by: Matthew Jacobs <mj@cloudera.com>
Tested-by: jenkins