Require codereview to have content (#18156)

- Report a validityError when the codeReview have no comment.
- Resolves #18151
- Refactor

web_src/js/features/repo-diff.js

@@ -1,5 +1,6 @@
 import {initCompReactionSelector} from './comp/ReactionSelector.js';
 import {initRepoIssueContentHistory} from './repo-issue-content.js';
+import {validateTextareaNonEmpty} from './comp/CommentEasyMDE.js';
 const {csrfToken} = window.config;
 
 export function initRepoDiffReviewButton() {
@@ -23,7 +24,13 @@ export function initRepoDiffFileViewToggle() {
 export function initRepoDiffConversationForm() {
   $(document).on('submit', '.conversation-holder form', async (e) => {
     e.preventDefault();
+
     const form = $(e.target);
+    const $textArea = form.find('textarea');
+    if (!validateTextareaNonEmpty(form, $textArea)) {
+      return;
+    }
+
     const newConversationHolder = $(await $.post(form.attr('action'), form.serialize()));
     const {path, side, idx} = newConversationHolder.data();