IMPALA-5031: remove undefined behavior: nullptr member function call
IMPALA-5031: remove undefined behavior: nullptr member function call

This member function call on a nullptr to a FragmentInstanceState was
present in data loading, end-to-end tests, and custom cluster tests.

Change-Id: I2377c14f7ea8f93bb96504dd2319c11ff709cd26
Reviewed-on: http://gerrit.cloudera.org:8080/6714
Reviewed-by: Michael Ho <43544f6c6f19372b140301f92a3768afc300868a@cloudera.com>
Tested-by: Impala Public Jenkins

cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala