RepositorySelect displays NO_REPOS on 404 (#547)

Test plan: Unit tests included, plus I manually tested it.

src/app/credExplorer/RepositorySelect.js

@@ -89,6 +89,9 @@ function repoStringToRepo(x: string): Repo {
 export async function loadStatus(localStore: LocalStore): Promise<Status> {
   try {
     const response = await fetch(REPO_REGISTRY_API);
+    if (response.status === 404) {
+      return {type: "NO_REPOS"};
+    }
     if (!response.ok) {
       console.error(response);
       return {type: "FAILURE"};

src/app/credExplorer/RepositorySelect.test.js

@@ -167,6 +167,13 @@ describe("app/credExplorer/RepositorySelect", () => {
         console.error = jest.fn();
       });
     });
+    it("returns NO_REPOS on fetch 404", () => {
+      fetch.mockResponseOnce("irrelevant", {status: 404});
+      expect.assertions(3);
+      return loadStatus(testLocalStore()).then((status) => {
+        expect(status).toEqual({type: "NO_REPOS"});
+      });
+    });
     it("loads selectedRepo from localStore, if available", () => {
       const repos = [
         {owner: "a", name: "b"},