Process instance suspend itself, the process instance can never be activated.

**Describe the bug**
When **I use a execution listener to suspend the current process instance**, all the executions, tasks, jobs will be suspended.
However, after the execution listener completed, **the process seems to create a new execution or task, and the new execution or task has not been suspended.**
By this time, **the process instance can never be activated**, beacuse when I try to activate the process, the new task has not been suspended, so it also can not be activated, and throw the FlowableException "Cannot set suspension state active for xxx : already in state active."
**What's more, I can't even delete the current process instance, because it is suspended.**

**Expected behavior**
However, I use Signal Intermediate Catching Event to implement my requirement.
But I think it is better to do a validation when execute the suspend commend, and if a process instance try to suspend itself, throw an exception to warn the user this error usage.

Beginne damit, dass sich eine Prozessinstanz aus einem Execution Listener heraus selbst suspendiert, und verfolge anschließend das Suspendieren sowie das nachfolgende Aktivieren oder Löschen. Als abgeschlossen gilt die Aufgabe, wenn der Suspend-Befehl diesen Fall der Selbstsuspendierung konsistent behandelt, einschließlich der erwarteten Warnung oder Exception, ohne nicht suspendierte Ausführungen oder Tasks zurückzulassen.

Vom Indexierungsmodell aus dem Issue-Text verfasst.