Description of problem:

If a drop filter is spec'd without an associated dropTestsSpec, CLO produces a nil pointer dereference

Version-Release number of selected component (if applicable):

Logging 5.9

How reproducible:

Always

Steps to Reproduce:

1. Create CLF:

   apiVersion: logging.openshift.io/v1
   kind: ClusterLogForwarder
   metadata:
     name: instance
     namespace: openshift-logging
   spec:
     filters:
     - name: my-drop
       type: drop
     pipelines:
     - filterRefs:
       - my-drop
       inputRefs:
       - application
       name: application-logs
       outputRefs:
       - default
   

Actual results:

Nil pointer dereference

Expected results:

validation error and rejection of CLF