MDEV-14333 Mariabackup --apply-log-only crashes if incomplete transactions...

MDEV-14333 Mariabackup --apply-log-only crashes if incomplete transactions with update_undo logs are present

trx_undo_free_prepared(): Relax the assertion for
mariabackup --apply-log-only.

mysql-test/suite/mariabackup/incremental_backup.result

 call mtr.add_suppression("InnoDB: New log files created");
-CREATE TABLE t(i INT) ENGINE INNODB;
+CREATE TABLE t(i INT PRIMARY KEY) ENGINE INNODB;
+BEGIN;
+INSERT INTO t VALUES(2);
+SET GLOBAL innodb_flush_log_at_trx_commit = 1;
 INSERT INTO t VALUES(1);
 # Create full backup , modify table, then create incremental/differential backup
-INSERT INTO t VALUES(2);
+BEGIN;
+INSERT INTO t VALUES(0);
+DELETE FROM t WHERE i=0;
+COMMIT;
 SELECT * FROM t;
 i
 1

mysql-test/suite/mariabackup/incremental_backup.test

@@ -4,23 +4,31 @@ call mtr.add_suppression("InnoDB: New log files created");
 let $basedir=$MYSQLTEST_VARDIR/tmp/backup;
 let $incremental_dir=$MYSQLTEST_VARDIR/tmp/backup_inc1;
 
-
-CREATE TABLE t(i INT) ENGINE INNODB;
+CREATE TABLE t(i INT PRIMARY KEY) ENGINE INNODB;
+BEGIN;
+INSERT INTO t VALUES(2);
+connect (con1,localhost,root,,);
+SET GLOBAL innodb_flush_log_at_trx_commit = 1;
 INSERT INTO t VALUES(1);
 
 echo # Create full backup , modify table, then create incremental/differential backup;
 --disable_result_log
 exec $XTRABACKUP --defaults-file=$MYSQLTEST_VARDIR/my.cnf  --backup --target-dir=$basedir;
 --enable_result_log
-INSERT INTO t VALUES(2);
+BEGIN;
+INSERT INTO t VALUES(0);
+DELETE FROM t WHERE i=0;
+connection default;
+COMMIT;
 SELECT * FROM t;
 exec $XTRABACKUP --defaults-file=$MYSQLTEST_VARDIR/my.cnf  --backup --target-dir=$incremental_dir --incremental-basedir=$basedir;
 
 --disable_result_log
 echo # Prepare full backup, apply incremental one;
 exec $XTRABACKUP --prepare --apply-log-only --target-dir=$basedir;
-exec $XTRABACKUP --prepare --target-dir=$basedir --incremental-dir=$incremental_dir ;
+exec $XTRABACKUP --prepare --apply-log-only --target-dir=$basedir --incremental-dir=$incremental_dir ;
 
+disconnect con1;
 echo # Restore and check results;
 let $targetdir=$basedir;
 -- source include/restart_and_restore.inc

storage/xtradb/trx/trx0undo.cc

@@ -2025,6 +2025,7 @@ trx_undo_free_prepared(
 			/* lock_trx_release_locks() assigns
 			trx->is_recovered=false */
 			ut_a(srv_read_only_mode
+			     || srv_apply_log_only
 			     || srv_force_recovery >= SRV_FORCE_NO_TRX_UNDO);
 			break;
 		default: