Hi Tom,
Yes, OOB dont have any conditions that would satisfy your requirement
I would suggest to do it, in script itself from where you are inititating workflow.
You can do below also but that would be generic.If you make that check then user might not be able to start any other workflow
"Node has no active workflow" OR "File in in BPM_package"
Rather than You can check specificically for your custom WF. If it is already active on Content then do NOT initiate new workflow.
You can use below API, you may check for similar JS API
//get all active WF on nodeRef . This will return you workflowInstance
workflowService.getWorkflowsForContent(nodeRef, true);
From workflowInstance, you can WorkflowDefinition and name/id of your workflow.
Hope this help!