Purging history / deleting outputs could fail workflow scheduling more gracefully

[galaxyproject-sentryintegration]

Not a big deal considering the outputs had been deleted

Sentry Issue: GALAXY-MAIN-118N

FileNotFoundError: [Errno 2] No such file or directory: ''
(1 additional frame(s) were not displayed)
...
  File "galaxy/workflow/run.py", line 255, in invoke
    incomplete_or_none = self._invoke_step(workflow_invocation_step)
  File "galaxy/workflow/run.py", line 344, in _invoke_step
    incomplete_or_none = invocation_step.workflow_step.module.execute(
  File "galaxy/workflow/modules.py", line 2384, in execute
    when_value = evaluate_value_from_expressions(
  File "galaxy/workflow/modules.py", line 226, in evaluate_value_from_expressions
    step_state[key] = to_cwl(value, hda_references=hda_references, step=step)
  File "galaxy/workflow/modules.py", line 158, in to_cwl
    with open(value.get_file_name()) as f:

Failed to execute scheduled workflow.