fix: prevents blank messages from being posted to chat (#8257)

* fix: throws an error when the server receives a post chat request with a message containing only whitespace.

* Adding a test confirming behavior around messages that only contain newlines.

* Removing accidental only that was left on a test

website/server/controllers/api-v3/chat.js

@@ -93,6 +93,7 @@ api.postChat = {
     let chatUpdated;
 
     req.checkParams('groupId', res.t('groupIdRequired')).notEmpty();
+    req.sanitize('message').trim();
     req.checkBody('message', res.t('messageGroupChatBlankMessage')).notEmpty();
 
     let validationErrors = req.validationErrors();