MDEV-18186 assertion failure on missing InnoDB index

This was introduced in 1a7a018
MDEV-16557 Remove INNOBASE_SHARE::idx_trans_tbl

ha_innobase::innobase_get_index: remove incorrect assertion.
Index nullability is checked in subsequent ifs.

Closes #1079

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

@@ -1892,3 +1892,19 @@ f1
 SELECT * FROM t2;
 f1
 DROP TABLE t1, t2;
+#
+#  MDEV-18186 assertion failure on missing InnoDB index
+#
+CREATE TABLE t (a INT, INDEX i1 (a)) ENGINE=INNODB;
+DROP TABLE t;
+CREATE TABLE t (a INT) ENGINE=INNODB;
+SHOW CREATE TABLE t;
+Table	Create Table
+t	CREATE TABLE `t` (
+  `a` int(11) DEFAULT NULL,
+  KEY `i1` (`a`)
+) ENGINE=InnoDB DEFAULT CHARSET=latin1
+Warnings:
+Warning	1082	InnoDB: Table test/t contains 0 indexes inside InnoDB, which is different from the number of indexes 1 defined in the MariaDB 
+Warning	1082	InnoDB: Table test/t contains 0 indexes inside InnoDB, which is different from the number of indexes 1 defined in the MariaDB 
+DROP TABLE t;

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

@@ -1151,6 +1151,28 @@ SELECT * FROM t2;
 
 DROP TABLE t1, t2;
 
+--echo #
+--echo #  MDEV-18186 assertion failure on missing InnoDB index
+--echo #
+
+--disable_query_log
+call mtr.add_suppression("Cannot find index i1 in InnoDB index dictionary");
+call mtr.add_suppression("InnoDB indexes are inconsistent with what defined");
+call mtr.add_suppression("Table test/t contains 0 indexes");
+call mtr.add_suppression("InnoDB could not find key no");
+--enable_query_log
+
+# Test an attempt to rename a nonexistent index inside InnoDB
+-- let $MYSQL_DATA_DIR = `SELECT @@datadir`
+CREATE TABLE t (a INT, INDEX i1 (a)) ENGINE=INNODB;
+-- copy_file $MYSQL_DATA_DIR/test/t.frm $MYSQL_DATA_DIR/test/t.fr_
+DROP TABLE t;
+CREATE TABLE t (a INT) ENGINE=INNODB;
+-- remove_file $MYSQL_DATA_DIR/test/t.frm
+-- move_file $MYSQL_DATA_DIR/test/t.fr_ $MYSQL_DATA_DIR/test/t.frm
+SHOW CREATE TABLE t;
+DROP TABLE t;
+
 --disable_query_log
 
 call mtr.add_suppression("InnoDB: Tablespace .* was not found at .*t[12].ibd.");

storage/innobase/handler/ha_innodb.cc

@@ -9534,7 +9534,6 @@ ha_innobase::innobase_get_index(
 	if (keynr != MAX_KEY && table->s->keys > 0) {
 		key = &table->key_info[keynr];
 		index = dict_table_get_index_on_name(ib_table, key->name);
-		ut_ad(index);
 	} else {
 		index = dict_table_get_first_index(ib_table);
 	}