pool-size = 0 will block DM task

[lance6716]

What did you do?

Will check if task config file will also trigger this bug, at lease the job which is created by service has this problem

What did you expect to see?

No response

What did you see instead?

No response

Versions of the cluster

DM version (run dmctl -V or dm-worker -V or dm-master -V):

(paste DM version here, and you must ensure versions of dmctl, DM-worker and DM-master are same)

Upstream MySQL/MariaDB server version:

(paste upstream MySQL/MariaDB server version here)

Downstream TiDB cluster version (execute SELECT tidb_version(); in a MySQL client):

(paste TiDB cluster version here)

How did you deploy DM: tiup or manually?

(leave TiUP or manually here)

Other interesting information (system version, hardware config, etc):

>
>

current status of DM cluster (execute query-status <task-name> in dmctl)

(paste current status of DM cluster here)

[fubinzh]

/severity moderate

[lance6716]

fixed by #7714