Partially restoring code removed by f7064be2 (Bug 2030: Timeout while uploading files to some FTP server using TLS 1.3)

https://winscp.net/tracker/2030
(cherry picked from commit b8e2cadde64fb9c0ca9b0130f5fd2ce4162e44e1)

Source commit: 78032fe3a2aaa65f76d448ba536d3fb6997e0f5c

source/filezilla/AsyncSslSocketLayer.cpp

@@ -1005,6 +1005,11 @@ BOOL CAsyncSslSocketLayer::ShutDown(int nHow /*=sends*/)
     }
 
     int res = SSL_shutdown(m_ssl);
+    if (res == 0)
+    {
+      // maybe we do not need to call this at all (as neon does)
+      SSL_shutdown(m_ssl);
+    }
     if (res >= 0)
     {
       if (ShutDownComplete())