Merge pull request #1494 from storybooks/1486-undo-channel-stubbing

Undo channel stubbing - causes NPM version errors to fail silently

lib/addons/src/index.js

@@ -1,8 +1,16 @@
+function channelError() {
+  throw new Error(
+    'Accessing nonexistent addons channel, see https://storybook.js.org/basics/faq/#why-is-there-no-addons-channel'
+  );
+}
+
 export class AddonStore {
   constructor() {
     this.loaders = {};
     this.panels = {};
-    this.channel = { on() {}, emit() {} };
+    // this.channel should get overwritten by setChannel if package versions are
+    // correct and AddonStore is a proper singleton. If not, throw an error.
+    this.channel = { on: channelError, emit: channelError };
     this.preview = null;
     this.database = null;
   }