ResourceBase: fix setDisableAutomaticItemDeliveryDone when the itemsync already exists.

E.g. because of calling setItemStreamingEnabled(true) first, which creates the
item sync with a copy of the "disable automatic item delivery done" setting,
which is still false at that point.

The only user of this method is the imap resource, which won't be affected
by this change.

REVIEW: 123472