sftp: fix proxy initialisation

This was being done in NewFs instead of NewFsWithConnection like it
should have been which meant calls to NewFsWithConnection were not
initialising the proxy correctly.

backend/sftp/sftp.go

@@ -925,15 +925,8 @@ func NewFs(ctx context.Context, name, root string, m configmap.Mapper) (fs.Fs, e
 		opt.Port = "22"
 	}
 
-	// get proxy URL if set
-	if opt.HTTPProxy != "" {
-		proxyURL, err := url.Parse(opt.HTTPProxy)
-		if err != nil {
-			return nil, fmt.Errorf("failed to parse HTTP Proxy URL: %w", err)
-		}
-		f.proxyURL = proxyURL
-	}
-
+	// Set up sshConfig here from opt
+	// **NB** everything else should be setup in NewFsWithConnection
 	sshConfig := &ssh.ClientConfig{
 		User:            opt.User,
 		Auth:            []ssh.AuthMethod{},
@@ -1181,11 +1174,21 @@ func NewFsWithConnection(ctx context.Context, f *Fs, name string, root string, m
 	f.mkdirLock = newStringLock()
 	f.pacer = fs.NewPacer(ctx, pacer.NewDefault(pacer.MinSleep(minSleep), pacer.MaxSleep(maxSleep), pacer.DecayConstant(decayConstant)))
 	f.savedpswd = ""
+
 	// set the pool drainer timer going
 	if f.opt.IdleTimeout > 0 {
 		f.drain = time.AfterFunc(time.Duration(f.opt.IdleTimeout), func() { _ = f.drainPool(ctx) })
 	}
 
+	// get proxy URL if set
+	if opt.HTTPProxy != "" {
+		proxyURL, err := url.Parse(opt.HTTPProxy)
+		if err != nil {
+			return nil, fmt.Errorf("failed to parse HTTP Proxy URL: %w", err)
+		}
+		f.proxyURL = proxyURL
+	}
+
 	f.features = (&fs.Features{
 		CanHaveEmptyDirectories:  true,
 		SlowHash:                 true,