MDEV-26621 assertion failue "index->table->persistent_autoinc" in...

MDEV-26621 assertion failue "index->table->persistent_autoinc" in /storage/innobase/btr/btr0btr.cc during IMPORT

dict_index_t::clear_instant_alter(): when searhing for an AUTO_INCREMENT column
don't skip the beginning of the list because the field can be at the beginning of the list

mysql-test/suite/innodb/r/instant_alter_import.result

@@ -70,3 +70,11 @@ select * from t1;
 ERROR HY000: Tablespace has been discarded for table `t1`
 drop table t2;
 drop table t1;
+CREATE TABLE t1 (id INT PRIMARY KEY AUTO_INCREMENT, i1 INT) ENGINE=INNODB;
+CREATE TABLE t2 (id INT PRIMARY KEY AUTO_INCREMENT, i1 INT, i2 INT) ENGINE=INNODB;
+ALTER TABLE t2 DROP COLUMN i2, ALGORITHM=INSTANT;
+ALTER TABLE t2 DISCARD TABLESPACE;
+FLUSH TABLE t1 FOR EXPORT;
+UNLOCK TABLES;
+ALTER TABLE t2 IMPORT TABLESPACE;
+DROP TABLE t2, t1;

mysql-test/suite/innodb/t/instant_alter_import.test

@@ -82,3 +82,22 @@ select * from t1;
 
 drop table t2;
 drop table t1;
+
+
+--let $MYSQLD_DATADIR= `SELECT @@datadir`
+
+CREATE TABLE t1 (id INT PRIMARY KEY AUTO_INCREMENT, i1 INT) ENGINE=INNODB;
+
+CREATE TABLE t2 (id INT PRIMARY KEY AUTO_INCREMENT, i1 INT, i2 INT) ENGINE=INNODB;
+ALTER TABLE t2 DROP COLUMN i2, ALGORITHM=INSTANT;
+ALTER TABLE t2 DISCARD TABLESPACE;
+
+FLUSH TABLE t1 FOR EXPORT;
+
+--copy_file $MYSQLD_DATADIR/test/t1.ibd $MYSQLD_DATADIR/test/t2.ibd
+--copy_file $MYSQLD_DATADIR/test/t1.cfg $MYSQLD_DATADIR/test/t2.cfg
+
+UNLOCK TABLES;
+ALTER TABLE t2 IMPORT TABLESPACE;
+
+DROP TABLE t2, t1;

storage/innobase/include/dict0mem.h

@@ -2440,7 +2440,7 @@ inline void dict_index_t::clear_instant_alter()
 			      { return a.col->ind < b.col->ind; });
 	table->instant = NULL;
 	if (ai_col) {
-		auto a = std::find_if(begin, end,
+		auto a = std::find_if(fields, end,
 				      [ai_col](const dict_field_t& f)
 				      { return f.col == ai_col; });
 		table->persistent_autoinc = (a == end) ? 0 : 1 + (a - fields);