IMPALA-1419, IMPALA-1542: Fix NullLiteral to reset its type in resetAnalysisState

Queries with arithmetic exprs containing a NullLiteral child failed (IMPALA-1419)
or crashed (IMPALA-1542) because re-analysis of these exprs was incorrect.

Change-Id: Ice3461aed53863123bcf8f38af123d89ad3b7d6a
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/5429
Reviewed-by: Matthew Jacobs <mj@cloudera.com>
Tested-by: jenkins