Bug #15598 Server crashes in specific case during setting new password

- Comparing host string against NULL caused crash. 
- If host.hostname is NULL treat it as ""


mysql-test/r/grant.result:
  Update test results
mysql-test/t/grant.test:
  Add test for user with host ""

mysql-test/r/grant.result

@@ -437,15 +437,6 @@ delete from mysql.columns_priv where user="mysqltest_3";
 flush privileges;
 drop database mysqltest_1;
 drop database mysqltest_2;
-insert into mysql.user (host, user) values ('', 'mysqltest_7');
-flush privileges;
-set password for mysqltest_7@ = password('systpass');
-show grants for mysqltest_7@;
-Grants for mysqltest_7@
-GRANT USAGE ON *.* TO 'mysqltest_7'@'' IDENTIFIED BY PASSWORD '*2FB071A056F9BB745219D9C876814231DAF46517'
-drop user mysqltest_7@;
-show grants for mysqltest_7@;
-ERROR 42000: There is no such grant defined for user 'mysqltest_7' on host ''
 SHOW PRIVILEGES;
 Privilege	Context	Comment
 Alter	Tables	To alter the table
@@ -624,3 +615,12 @@ show grants for root@localhost;
 Grants for root@localhost
 GRANT ALL PRIVILEGES ON *.* TO 'root'@'localhost' WITH GRANT OPTION
 set names latin1;
+create user mysqltest_7@;
+set password for mysqltest_7@ = password('systpass');
+show grants for mysqltest_7@;
+Grants for mysqltest_7@
+GRANT USAGE ON *.* TO 'mysqltest_7'@'' IDENTIFIED BY PASSWORD '*2FB071A056F9BB745219D9C876814231DAF46517'
+drop user mysqltest_7@;
+flush privileges;
+show grants for mysqltest_7@;
+ERROR 42000: There is no such grant defined for user 'mysqltest_7' on host ''

mysql-test/t/grant.test

@@ -503,11 +503,11 @@ set names latin1;
 # Bug #15598 Server crashes in specific case during setting new password
 # - Caused by a user with host ''
 #
-insert into mysql.user (host, user) values ('', 'mysqltest_7');
-flush privileges;
+create user mysqltest_7@;
 set password for mysqltest_7@ = password('systpass');
 show grants for mysqltest_7@;
 drop user mysqltest_7@;
+flush privileges; # BUG#16297(flush should be removed when that bug is fixed)
 --error 1141
 show grants for mysqltest_7@;