Don't allow posting again while previous hasn't returned

src/components/post_status_form/post_status_form.js

@@ -87,6 +87,7 @@ const PostStatusForm = {
       this.caret = selectionStart
     },
     postStatus (newStatus) {
+      if (this.posting) { return }
       this.posting = true
       statusPoster.postStatus({
         status: newStatus.status,