Limit impact of e78c2485 to TLS 1.3 only

https://winscp.net/tracker/1834

Source commit: d4f10f2624093a4781a579b8c041b64c9d6661c4

source/filezilla/AsyncSslSocketLayer.cpp

@@ -986,6 +986,11 @@ BOOL CAsyncSslSocketLayer::ShutDown(int nHow /*=sends*/)
     if (res == 0)
     {
       res = SSL_shutdown(m_ssl);
+      // While this should not be necessary, with IIS we get timeout otherwise
+      if (SSL_version(m_ssl) <= TLS1_2_VERSION)
+      {
+        res = 0;
+      }
     }
     if (res >= 0)
     {