fix: 当上一串消息不存在文本时then默认使用本段

Signed-off-by: 502647092 <admin@yumc.pw>

src/main/java/pw/yumc/YumCore/tellraw/Tellraw.java

@@ -301,8 +301,9 @@ public class Tellraw {
         final MessagePart last = latest();
         if (!last.hasText()) {
             last.text = part.text;
-        }
+        } else {
             messageParts.add(part);
+        }
         return this;
     }
 }