MDEV-32449 Server crashes in Alter_info::add_stat_drop_index upon CREATE TABLE

Fixed missing initialization of Alter_info()

This could cause crashes in some create table like scenarios
where some generated indexes where automatically dropped.

I also added a test that we do not try to drop from index_stats for
temporary tables.

mysql-test/main/alter_table.result

@@ -3093,3 +3093,31 @@ drop table t1;
 #
 # End of 10.5 tests
 #
+#
+# MDEV-32449 Server crashes in Alter_info::add_stat_drop_index upon CREATE TABLE
+#
+CREATE TABLE t1 (
+`altcol1` blob DEFAULT '',
+KEY `altcol1` (`altcol1`(2300))
+) ROW_FORMAT=PAGE, ENGINE=Aria;
+ALTER TABLE t1 ADD FOREIGN KEY h (`altcol1`) REFERENCES t1 (`altcol1`) ON UPDATE SET DEFAULT, ALGORITHM=COPY;
+Warnings:
+Note	1071	Specified key was too long; max key length is 2300 bytes
+create or replace table t2 like t1;
+show create table t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `altcol1` blob DEFAULT '',
+  KEY `altcol1` (`altcol1`(2300)),
+  KEY `h` (`altcol1`(2300))
+) ENGINE=Aria DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci PAGE_CHECKSUM=1 ROW_FORMAT=PAGE
+show create table t2;
+Table	Create Table
+t2	CREATE TABLE `t2` (
+  `altcol1` blob DEFAULT '',
+  KEY `altcol1` (`altcol1`(2300))
+) ENGINE=Aria DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci PAGE_CHECKSUM=1 ROW_FORMAT=PAGE
+drop table t1,t2;
+#
+# End of 10.6 tests
+#

mysql-test/main/alter_table.test

@@ -2382,3 +2382,21 @@ drop table t1;
 --echo #
 --echo # End of 10.5 tests
 --echo #
+
+--echo #
+--echo # MDEV-32449 Server crashes in Alter_info::add_stat_drop_index upon CREATE TABLE
+--echo #
+
+CREATE TABLE t1 (
+  `altcol1` blob DEFAULT '',
+  KEY `altcol1` (`altcol1`(2300))
+) ROW_FORMAT=PAGE, ENGINE=Aria;
+ALTER TABLE t1 ADD FOREIGN KEY h (`altcol1`) REFERENCES t1 (`altcol1`) ON UPDATE SET DEFAULT, ALGORITHM=COPY;
+create or replace table t2 like t1;
+show create table t1;
+show create table t2;
+drop table t1,t2;
+
+--echo #
+--echo # End of 10.6 tests
+--echo #

sql/sql_alter.h

@@ -199,6 +199,7 @@ class Alter_info
   Alter_info() :
   flags(0), partition_flags(0),
     keys_onoff(LEAVE_AS_IS),
+    original_table(0),
     num_parts(0),
     requested_algorithm(ALTER_TABLE_ALGORITHM_NONE),
     requested_lock(ALTER_TABLE_LOCK_DEFAULT)

sql/sql_table.cc

@@ -2898,7 +2898,7 @@ mysql_prepare_create_table(THD *thd, HA_CREATE_INFO *create_info,
   key_iterator.rewind();
   while ((key=key_iterator++))
   {
-    if (key->type == Key::IGNORE_KEY)
+    if (key->type == Key::IGNORE_KEY && !create_info->tmp_table())
     {
       /* The key was replaced by another key */
       if (alter_info->add_stat_drop_index(thd, &key->name))