Solve race condition for test path filtering

[armenzg]

During review time we introduced a small bug in the test filtering feature.

Reading jobList at the begining of the function instead of just before calling mapPushJobs almost guaranteed to start with an empty list which makes the call useless since it needs a non-empty list to work.

I also changed the code to call this.setState with a callback to mapPushJobs to guarantee that jobTypeNameToManifests is set in the state and not get an empty object.

diff --git a/ui/job-view/pushes/Push.jsx b/ui/job-view/pushes/Push.jsx
index 8e0e96547..0a79c394a 100644
--- a/ui/job-view/pushes/Push.jsx
+++ b/ui/job-view/pushes/Push.jsx
@@ -163,15 +163,18 @@ class Push extends React.PureComponent {

   fetchTestManifests = async () => {
     const { currentRepo, push } = this.props;
-    const { jobList } = this.state;

     const jobTypeNameToManifests = await fetchTestManifests(
       currentRepo.name,
       push.revision,
     );
-    this.setState({ jobTypeNameToManifests });
-    // This adds to the jobs the test_path property
-    this.mapPushJobs(jobList);
+    // Call setState with callback to guarantee the state of jobTypeNameToManifest
+    // to be set since it is read within mapPushJobs and we might have a race
+    // condition. We are also reading jobList now rather than before fetching
+    // the artifact because it gives us an empty list
+    this.setState({
+      jobTypeNameToManifests,
+    }, () => this.mapPushJobs(this.state.jobList));
   };