Fix a bug with author name

Signed-off-by: Mario Danic <mario@lovelyhq.com>

app/src/main/java/com/nextcloud/talk/adapters/messages/MagicIncomingTextMessageViewHolder.java

@@ -47,7 +47,7 @@ public class MagicIncomingTextMessageViewHolder
     public void onBind(ChatMessage message) {
         super.onBind(message);
         String author;
-        if (TextUtils.isEmpty(author = message.getActorDisplayName())) {
+        if (!TextUtils.isEmpty(author = message.getActorDisplayName())) {
             messageAuthor.setText(author);
         } else {
             messageAuthor.setText(R.string.nc_nick_guest);