Bug 1957: SFTP uploads are slow

https://winscp.net/tracker/1957
(cherry picked from commit 7ed4e1b41196a232c1a38b5be2d6855df815d592)

Source commit: f8cd8fb95a1f4020da72f7520edd114673cc8d6e

source/putty/ssh.c

@@ -1006,8 +1006,12 @@ static size_t ssh_sendbuffer(Backend *be)
 
     backlog = ssh_stdin_backlog(ssh->cl);
 
+    #ifndef WINSCP
+    // This throttles WinSCP unnecessarily, as it uses its own throttling mechanism.
+    // This value is used only by WinSCP, never directly by PuTTY code.
     if (ssh->base_layer)
         backlog += ssh_ppl_queued_data_size(ssh->base_layer);
+    #endif
 
     /*
      * If the SSH socket itself has backed up, add the total backup