[explore] allow URL shortner even if no slice exist (#4457)

recent regression perhaps from the PR that moved to using POST .

superset/assets/spec/javascripts/explore/components/ExploreActionButtons_spec.jsx

@@ -8,12 +8,7 @@ import ExploreActionButtons from
 describe('ExploreActionButtons', () => {
   const defaultProps = {
     canDownload: 'True',
-    slice: {
-      data: {
-        csv_endpoint: '',
-        json_endpoint: '',
-      },
-    },
+    latestQueryFormData: {},
     queryEndpoint: 'localhost',
   };