[likes] Don't send liked notification for posts without plain content.#4095

YUCLing wants to merge 2 commits intoflarum:2.xflarum/framework:2.xfrom

YUCLing:fix/non-string-content-post-likes-notificationYUCLing/flarum-framework:fix/non-string-content-post-likes-notificationCopy head branch name to clipboard