[windows] Fix dialog icon

v3/pkg/w32/dialogs.go

@@ -11,7 +11,7 @@ func MessageBoxWithIcon(hwnd HWND, text *uint16, caption *uint16, iconID int, fl
 	params := MSGBOXPARAMS{
 		cbSize:      uint32(unsafe.Sizeof(MSGBOXPARAMS{})),
 		hwndOwner:   hwnd,
-		hInstance:   0,
+		hInstance:   GetApplicationHandle(),
 		lpszText:    text,
 		lpszCaption: caption,
 		dwStyle:     flags,

v3/pkg/w32/kernel32.go

@@ -60,6 +60,11 @@ func GetModuleHandle(modulename string) HINSTANCE {
 	return HINSTANCE(ret)
 }
 
+func GetApplicationHandle() HINSTANCE {
+	ret, _, _ := procGetModuleHandle.Call(0)
+	return ret
+}
+
 func MulDiv(number, numerator, denominator int) int {
 	ret, _, _ := procMulDiv.Call(
 		uintptr(number),