Comment 2 for bug 783530

Partially-simplified test case. May contain queries that are not relevant. Run with valgrind to get the following warning (among others):

==21196== Invalid read of size 1
==21196== at 0x803EDC: hp_extract_record (in /home/philips/bzr/mysql-55-eb-release/sql/mysqld)
==21196== by 0x80443F: heap_scan (in /home/philips/bzr/mysql-55-eb-release/sql/mysqld)
==21196== by 0x7FFA9E: ha_heap::rnd_next(unsigned char*) (in /home/philips/bzr/mysql-55-eb-release/sql/mysqld)
==21196== by 0x745B2E: rr_sequential(READ_RECORD*) (in /home/philips/bzr/mysql-55-eb-release/sql/mysqld)
==21196== by 0x5E6548: mysql_update(THD*, TABLE_LIST*, List<Item>&, List<Item>&, Item*, unsigned int, st_order*, unsigned long long, enum_duplicates, bool,
 unsigned long long*, unsigned long long*) (in /home/philips/bzr/mysql-55-eb-release/sql/mysqld)
==21196== by 0x576CA1: mysql_execute_command(THD*) (in /home/philips/bzr/mysql-55-eb-release/sql/mysqld)
==21196== by 0x57A179: mysql_parse(THD*, char*, unsigned int, Parser_state*) (in /home/philips/bzr/mysql-55-eb-release/sql/mysqld)
==21196== by 0x57B523: dispatch_command(enum_server_command, THD*, char*, unsigned int) (in /home/philips/bzr/mysql-55-eb-release/sql/mysqld)
==21196== by 0x613F12: do_handle_one_connection(THD*) (in /home/philips/bzr/mysql-55-eb-release/sql/mysqld)
==21196== by 0x613FBB: handle_one_connection (in /home/philips/bzr/mysql-55-eb-release/sql/mysqld)
==21196== by 0x7FCCD5: pfs_spawn_thread (in /home/philips/bzr/mysql-55-eb-release/sql/mysqld)
==21196== by 0x35A7207760: start_thread (in /lib64/libpthread-2.12.2.so)
==21196== by 0xFA526FF: ???
==21196== Address 0xbec6a28 is not stack'd, malloc'd or (recently) free'd