Better robustness when action loading fails.
For example, the following should not cause Run.onLoad itself to fail:
java.lang.NullPointerException
	at org.jenkinsci.plugins.workflow.steps.input.InputAction.onLoad(InputAction.java:29)
	at hudson.model.Run.onLoad(Run.java:342)
	at org.jenkinsci.plugins.workflow.job.WorkflowRun.onLoad(WorkflowRun.java:332)