Add default array for RichContent emoji

Reports don't currently return an emoji key. There's an MR to add it, but in case something doesn't return this key, we now have a default empty array.

src/components/rich_content/rich_content.jsx

@@ -42,7 +42,8 @@ export default Vue.component('RichContent', {
     // Emoji object, as in status.emojis, note the "s" at the end...
     emoji: {
       required: true,
-      type: Array
+      type: Array,
+      default: () => []
     },
     // Whether to handle links or not (posts: yes, everything else: no)
     handleLinks: {