IMPALA-4350: Crash with vlog level 2 in hash join node
IMPALA-4350: Crash with vlog level 2 in hash join node

Testing:
Reproduced by running test_mem_usage_scaling against an Impala with
-v=2. Confirmed the fix avoided the crash.

We don't have any routine testing of high log levels so there isn't
a clear way to get good coverage of all code paths where there might be
similar bugs.

Change-Id: Ieedd49d8a17709177a622ddc15b78a3f48e12d3f
Reviewed-on: http://gerrit.cloudera.org:8080/4830
Reviewed-by: Tim Armstrong <2f8e34250f03a653da3dc27f7ec203eafdde80fc@cloudera.com>
Tested-by: Internal Jenkins

cloudera/Impala,michaelhkw/incubator-impala,cloudera/Impala,michaelhkw/incubator-impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala,michaelhkw/incubator-impala,cloudera/Impala,michaelhkw/incubator-impala,cloudera/Impala,michaelhkw/incubator-impala