MDEV-32025 Crashes in MDL_key::mdl_key_init with lower-case-table-names=2

Backporting a part of MDEV-32026 (which also fixed MDEV-32025 in 11.3)
from 11.3 to 10.4.

The reported crash happened with --lower-case-table-names=2
on statements like:

ALTER DATABASE Db1 DEFAULT CHARACTER SET utf8;
ALTER DATABASE `#mysql50#D+b1` UPGRADE DATA DIRECTORY NAME;

lock_schema_name() expects a normalized database name
and assert if a non-normalized name comes.

mysql_alter_db_internal() and mysql_upgrade_db() get
a non-normalized database name in the parameter.
Fixing them to normalize the database name before passing
it to lock_schema_name().

mysql-test/main/lowercase_table2.result

@@ -358,3 +358,24 @@ disconnect conn1;
 drop user 'mysqltest_1'@'localhost';
 drop tables a, B;
 drop database db1;
+#
+# MDEV-32025 Crashes in MDL_key::mdl_key_init with lower-case-table-names=2
+#
+CREATE DATABASE `#mysql50#D+b1`;
+ALTER DATABASE `#mysql50#D+b1` UPGRADE DATA DIRECTORY NAME;
+SHOW CREATE DATABASE `D+b1`;
+Database	Create Database
+D+b1	CREATE DATABASE `D+b1` /*!40100 DEFAULT CHARACTER SET latin1 COLLATE latin1_swedish_ci */
+SHOW CREATE DATABASE `d+b1`;
+Database	Create Database
+d+b1	CREATE DATABASE `d+b1` /*!40100 DEFAULT CHARACTER SET latin1 COLLATE latin1_swedish_ci */
+DROP DATABASE `D+b1`;
+CREATE DATABASE Db1;
+ALTER DATABASE Db1 DEFAULT CHARACTER SET utf8;
+SHOW CREATE DATABASE Db1;
+Database	Create Database
+Db1	CREATE DATABASE `Db1` /*!40100 DEFAULT CHARACTER SET utf8 COLLATE utf8_general_ci */
+SHOW CREATE DATABASE db1;
+Database	Create Database
+db1	CREATE DATABASE `db1` /*!40100 DEFAULT CHARACTER SET utf8 COLLATE utf8_general_ci */
+DROP DATABASE Db1;

mysql-test/main/lowercase_table2.test

@@ -313,4 +313,20 @@ connection default;
 disconnect conn1;
 drop user 'mysqltest_1'@'localhost';
 drop tables a, B;
-drop database db1;
\ No newline at end of file
+drop database db1;
+
+--echo #
+--echo # MDEV-32025 Crashes in MDL_key::mdl_key_init with lower-case-table-names=2
+--echo #
+
+CREATE DATABASE `#mysql50#D+b1`;
+ALTER DATABASE `#mysql50#D+b1` UPGRADE DATA DIRECTORY NAME;
+SHOW CREATE DATABASE `D+b1`;
+SHOW CREATE DATABASE `d+b1`;
+DROP DATABASE `D+b1`;
+
+CREATE DATABASE Db1;
+ALTER DATABASE Db1 DEFAULT CHARACTER SET utf8;
+SHOW CREATE DATABASE Db1;
+SHOW CREATE DATABASE db1;
+DROP DATABASE Db1;

sql/sql_db.cc

@@ -715,7 +715,10 @@ mysql_alter_db_internal(THD *thd, const LEX_CSTRING *db,
   int error= 0;
   DBUG_ENTER("mysql_alter_db");
 
-  if (lock_schema_name(thd, db->str))
+  char dbnorm_buffer[SAFE_NAME_LEN + 1];
+  const char *dbnorm= normalize_db_name(db->str, dbnorm_buffer,
+                                        sizeof(dbnorm_buffer));
+  if (lock_schema_name(thd, dbnorm))
     DBUG_RETURN(TRUE);
 
   /* 
@@ -1686,8 +1689,12 @@ bool mysql_upgrade_db(THD *thd, const LEX_CSTRING *old_db)
   new_db.str= old_db->str + MYSQL50_TABLE_NAME_PREFIX_LENGTH;
   new_db.length= old_db->length - MYSQL50_TABLE_NAME_PREFIX_LENGTH;
 
+  char dbnorm_buffer_old[SAFE_NAME_LEN + 1];
+  const char *old_dbnorm= normalize_db_name(old_db->str, dbnorm_buffer_old,
+                                            sizeof(dbnorm_buffer_old));
+
   /* Lock the old name, the new name will be locked by mysql_create_db().*/
-  if (lock_schema_name(thd, old_db->str))
+  if (lock_schema_name(thd, old_dbnorm))
     DBUG_RETURN(1);
 
   /*