Fix saving the node document at the end of an escalation rule

Modifications done by an escalation rule to a node document are not flushed because the document model is saved without being re-fetched at the end of the worker.

A case to reproduce:

• have a simple workflow with a transition looping on a task node
• from an escalation rule, force the resume of the workflow => each time this rule is executed, the existing task is canceled and a new one is created, so the property "rnode:tasks_info" should contain these tasks. Instead, the node document always keeps the reference to only the first task.