修复rename错误

zen-core/src/main/kotlin/com/gxzc/zen/common/util/UploadUtil.kt

@@ -261,7 +261,7 @@ object UploadUtil {
         } else {
             // 后缀
             val ext = FilenameUtils.getExtension(rename)
-            if (ext == null) {
+            if (ext.isNullOrEmpty()) {
                 "$rename.${FilenameUtils.getExtension(filename)}"
             } else {
                 rename