fix upload message isEmpty

src/main/java/com/yutou/qqbot/Controllers/AppController.java

@@ -61,6 +61,9 @@ public class AppController {
     public String sendQQ(@RequestBody JSONObject json) {
         File image = null;
         String ret;
+        if(json.getString("message").isEmpty()){
+            return "not message";
+        }
         if (json.containsKey("image")) {
             image = HttpTools.syncDownload(json.getString("image"), System.currentTimeMillis() + ".png");
         }