When "mariabackup --target-dir=$basedir --incremental-dir=$incremental_dir"
is running and is moving a new table file (e.g. `db1/t1.new`) from the
incremental directory to the base directory, it needs to verify that the base
backup database directory (e.g. `$basedir/db1`) really exists
(or create it otherwise).
The table `db1/t1` can come from a new database `db1` which
was created during the base mariabackup execution time.
In such case the directory `db1` exists only in the incremental directory,
but does not exist in the base directory.
