Base-64 字符数组或字符串的长度无效等问题解决方案，base-64数组
string dummyData = base64.Trim().Replace("%", "").Replace(",", "").Replace(" ", "+");
if (dummyData.Length % 4 > 0)
{
dummyData = dummyDaaseta.PadRight(dummyData.Length + 4 - dummyData.Length % 4, '=');
}
MemoryStream stream = new MemoryStream(Convert.FromBase64String(dummyData));