MDEV-13818 CREATE INDEX leaks memory if running out of undo log space

free already allocated indexes if row_merge_create_index() fails

This fixes innodb.alter_crash failure
in ASAN_OPTIONS="abort_on_error=1" runs

storage/innobase/handler/handler0alter.cc

@@ -4860,7 +4860,7 @@ prepare_inplace_alter_table_dict(
 
 	/* Create the indexes in SYS_INDEXES and load into dictionary. */
 
-	for (ulint a = 0; a < ctx->num_to_add_index; a++) {
+	for (int a = 0; a < ctx->num_to_add_index; a++) {
 
 		if (index_defs[a].ind_type & DICT_VIRTUAL
 		    && ctx->num_to_drop_vcol > 0 && !new_clustered) {
@@ -4877,6 +4877,9 @@ prepare_inplace_alter_table_dict(
 		if (!ctx->add_index[a]) {
 			error = ctx->trx->error_state;
 			DBUG_ASSERT(error != DB_SUCCESS);
+			while (--a >= 0) {
+				dict_mem_index_free(ctx->add_index[a]);
+			}
 			goto error_handling;
 		}
 

storage/innobase/row/row0merge.cc

@@ -4418,6 +4418,7 @@ row_merge_create_index(
 		this index, to ensure read consistency. */
 		ut_ad(index->trx_id == trx->id);
 	} else {
+		dict_mem_index_free(index);
 		index = NULL;
 	}