动态随机换图，上传后还原图片和标题功能

AllBase/Helper/DataOpenSSL.cs

@@ -76,6 +76,9 @@ namespace AllBase.Helper
 
         public static string DecryptString(string cipherText)
         {
+            if (cipherText == null)
+                return null;
+
             cipherText = cipherText.Replace("-", "+").Replace("_", "/");
             var x1 = cipherText.Length % 4;
             if (x1 > 0)