fix(printer): 处理空人脸样本导致的异常

- 添加空人脸样本检查，避免空指针异常
- 当人脸样本不存在时，设置响应状态为404
- 提前返回，防止后续逻辑执行

src/main/java/com/ycwl/basic/controller/printer/PrinterTvController.java

@@ -72,6 +72,10 @@ public class PrinterTvController {
         File qrcode = new File("qrcode_"+sampleId+".jpg");
         try {
             FaceSampleEntity faceSample = faceRepository.getFaceSample(sampleId);
+            if (faceSample == null) {
+                response.setStatus(404);
+                return;
+            }
             MpConfigEntity scenicMpConfig = scenicRepository.getScenicMpConfig(faceSample.getScenicId());
             WxMpUtil.generateUnlimitedWXAQRCode(scenicMpConfig.getAppId(), scenicMpConfig.getAppSecret(), "pages/printer/from_sample", sampleId.toString(), qrcode);