Fix Bug #21328 mysqld issues warnings on ALTER CSV table to MyISAM

mysql-test/r/csv.result:
  update result file
mysql-test/r/log_tables.result:
  log_tables test contains alter of a CSV table with
  NULLs which results in warnings. In fact this is how
  the bug noticed. So, now when it is fixed we should
  update result file.
mysql-test/t/csv.test:
  add a test for the bug
storage/csv/ha_tina.cc:
  We should write 0 to the data file in the
  case we meet NULL. CSV does not support
  NULL values internally and we shouldn't
  distinguish them from 0 when writing a row
  (the alternative is to implement full NULL
  support). Otherwise other routines (such as
  Field::check_int() become confused).
  In 5.0 NULLs are stored as zeroes. In 5.1 it
  somehow turned into empty string. Which is wrong.

1 files changed, 8 insertions, 0 deletions

diff --git a/mysql-test/r/csv.result b/mysql-test/r/csv.result
index 32ca47e20d2..12cf900046f 100644
--- a/mysql-test/r/csv.result
+++ b/mysql-test/r/csv.result
@@ -5223,3 +5223,11 @@ check table bug22080_3;
 Table	Op	Msg_type	Msg_text
 test.bug22080_3	check	error	Corrupt
 drop tables bug22080_1,bug22080_2,bug22080_3;
+CREATE TABLE `bug21328` (
+`col1` int(11) DEFAULT NULL,
+`col2` int(11) DEFAULT NULL,
+`col3` int(11) DEFAULT NULL
+) ENGINE=CSV;
+insert into bug21328 values (1,NULL,NULL);
+alter table bug21328 engine=myisam;
+drop table bug21328;