fix cvm npe (#1618)

* fix cvm npe

* add changelog

---------

Co-authored-by: mikatong <mikatong@tencent.com>

Author: tongyiming

.changelog/1618.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+resource/tencentcloud_instance: fix npe
+```

tencentcloud/resource_tc_instance.go

@@ -919,15 +919,15 @@ func resourceTencentCloudInstanceRead(d *schema.ResourceData, meta interface{})
 	err = resource.Retry(readRetryTimeout, func() *resource.RetryError {
 		request := cvm.NewDescribeImagesRequest()
 		response, errRet = client.UseCvmClient().DescribeImages(request)
+		if errRet != nil {
+			return retryError(errRet, InternalError)
+		}
 		if *response.Response.TotalCount > 0 {
 			for i := range response.Response.ImageSet {
 				image := response.Response.ImageSet[i]
 				cvmImages = append(cvmImages, *image.ImageId)
 			}
 		}
-		if errRet != nil {
-			return retryError(errRet, InternalError)
-		}
 		return nil
 	})