Wait for workspace initialization before registering menu items

apps/remix-ide/src/remixAppManager.js

@@ -135,6 +135,7 @@ export class RemixAppManager extends PluginManager {
   }
 
   async registerContextMenuItems () {
+    this.on('filePanel', 'workspaceInitializationCompleted', async () => {
       await this.call('filePanel', 'registerContextMenuItem', {
         id: 'flattener',
         name: 'flattenFileCustomAction',
@@ -155,6 +156,7 @@ export class RemixAppManager extends PluginManager {
         pattern: [],
         sticky: true
       })
+    })
   }
 }