Truly ignore failures in skimage.

tools/tests/skimage/input/bad-images/empty-results.json

 {
    "actual-results" : {
       "failed" : null,
       "failure-ignored" : null,
       "no-comparison" : null,
       "succeeded" : null
    },
-   "expected-results" : null
+   "expected-results" : {
+      "invalid.png" : {
+      }
+   }
 }