Add forgotten wxUSE_VALIDATORS checks

Compilation with wxUSE_VALIDATORS==0 would have failed after the recent
changes, so fix this by adding the missing check.

See #23312.

(cherry picked from commit 623591823d503a46a843503c126d2bfc542fef3f)

src/generic/datectlg.cpp

@@ -54,6 +54,8 @@
 namespace
 {
 
+#if wxUSE_VALIDATORS
+
 class DateValidator : public wxValidator
 {
 public:
@@ -108,6 +110,8 @@ private:
     const wxString m_format;
 };
 
+#endif // wxUSE_VALIDATORS
+
 } // anonymous namespace
 
 class wxCalendarComboPopup : public wxCalendarCtrl,