Fix 3D canvas blank area during window resize after wxWidgets 3.3.2 upgrade

src/slic3r/GUI/GLCanvas3D.cpp

@@ -4739,11 +4739,19 @@ void GLCanvas3D::on_mouse(wxMouseEvent& evt)
 
 void GLCanvas3D::on_paint(wxPaintEvent& evt)
 {
-    if (m_initialized)
+    if (m_initialized) {
+#ifdef __WXMSW__
+        // Idle events are not dispatched during the Windows resize modal loop,
+        // so render immediately to avoid blank frames.
+        _refresh_if_shown_on_screen();
+        m_dirty = false;
+#else
         m_dirty = true;
-    else
+#endif
+    } else {
         // Call render directly, so it gets initialized immediately, not from On Idle handler.
         this->render();
+    }
 }
 
 void GLCanvas3D::force_set_focus() {