MDEV-11730 Memory leak in innodb.innodb_corrupt_bit

Memory was leaked when ALTER TABLE is attempted on a table
that contains corrupted indexes.
The memory leak was reported by AddressSanitizer for the test
innodb.innodb_corrupt_bit. The leak was introduced into
MariaDB Server 10.0.26, 10.1.15, 10.2.1 by the following:

commit c081c978
Merge: 1d21b221 a482e76e
Author: Sergei Golubchik <serg@mariadb.org>
Date:   Tue Jun 21 14:11:02 2016 +0200

   Merge branch '5.5' into bb-10.0

storage/innobase/handler/handler0alter.cc

@@ -3890,7 +3890,7 @@ ha_innobase::prepare_inplace_alter_table(
 					index->name, TRUE);
 
 				my_error(ER_INDEX_CORRUPT, MYF(0), index_name);
-				DBUG_RETURN(true);
+				goto err_exit;
 			}
 		}
 	}

storage/xtradb/handler/handler0alter.cc

@@ -3904,7 +3904,7 @@ ha_innobase::prepare_inplace_alter_table(
 					index->name, TRUE);
 
 				my_error(ER_INDEX_CORRUPT, MYF(0), index_name);
-				DBUG_RETURN(true);
+				goto err_exit;
 			}
 		}
 	}