fix: InviteController 登录态校验防御 null userId

cfc-backend/src/main/java/com/etotem/cfc/controller/InviteController.java

@@ -64,6 +64,9 @@ public class InviteController {
 
     @PostMapping("/qrcode")
     public Result<Map<String, Object>> getQrCode(@RequestAttribute("userId") Long userId) {
+        if (userId == null || userId <= 0) {
+            return Result.error("请先登录");
+        }
         try {
             String referralCode = commissionService.getOrCreateReferralCode(userId);
             String qrBase64 = wechatService.generateWxacode("ref=" + referralCode, "pages/invite/join");