[DBClientAction] Add a workaround for broken isIncidentSenderEnabled()

It always returns false when the first action in DB is invalid
(the corresponding incident tracker doesn't exist).

The root cause is the validator in getActionList(). It may drop
fetched records, so it conflicts with "LIMIT" clause of SQL.
We should fix getActionList() side to resolve this issue completely.
Merge pull request #351 from project-hatohol/workaround-checking-active-issue-sender

[DBClientAction] Add a workaround for broken isIncidentSenderEnabled()