IMPALA-5261: Heap use-after-free in HdfsSequenceTableWriter
IMPALA-5261: Heap use-after-free in HdfsSequenceTableWriter

HdfsSequenceTableWriter::ConsumeRow() function dereferenced a pointer
that pointed to a previously deallocated memory (which belonged to an
out of scope string object). This caused the ASAN build to fail.

The fix was verified by running TestTableWriters.test_seq_writer and
TestTableWriters.test_seq_writer_hive_compatibility end-to-end tests
against the ASAN build. These tests consistently crashed impalad
before the fix.

Change-Id: Id339247f892710529d8ad56dd1e98eadbf32900b
Reviewed-on: http://gerrit.cloudera.org:8080/6762
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