Fix UI code generation using ui2walk.

connectdialog_windows.go

@@ -1,5 +1,4 @@
 //+build windows
-//go:generate ui2walk connectdialog.ui
 
 package main
 

dialog_windows.go

@@ -1,11 +1,8 @@
 //+build windows
-//go:generate ui2walk dialog.ui
 
 package main
 
-import (
-	"github.com/lxn/walk"
-)
+import "github.com/lxn/walk"
 
 type mainDialog struct {
 	*walk.MainWindow

main_windows.go

@@ -1,6 +1,9 @@
 //+build windows
+
 package main
 
+//go:generate ui2walk
+
 import (
 	"fmt"
 	"log"