fix: pass correct menu item index in WM_INITMENUPOPUP lParam for submenus

Previously, WM_INITMENUPOPUP was sent with lParam=0xFFFFFFFF for all
submenus, which tells the context menu handler that the menu position
is unknown. This caused the SendTo shell extension to fail to properly
identify the submenu, resulting in it enumerating the wrong directory
(user home directory instead of the SendTo folder).

Now we pass the actual menu item index as the low-order word of lParam,
allowing context menu handlers to correctly identify which submenu is
being initialized.

Author: lidaixingchen

src/shell/contextmenu/contextmenu.cc

@@ -177,11 +177,12 @@ menu menu::construct_with_hmenu(
 
         if (info.hSubMenu) {
             auto main_thread_id = GetCurrentThreadId();
+            int submenu_pos = i;
             item.submenu = [=](std::shared_ptr<menu_widget> mw) {
                 auto task = [&]() {
                     HandleMenuMsg(WM_INITMENUPOPUP,
                                   reinterpret_cast<WPARAM>(info.hSubMenu),
-                                  0xFFFFFFFF);
+                                  static_cast<LPARAM>(submenu_pos));
                     mw->init_from_data(menu::construct_with_hmenu(
                         info.hSubMenu, hWnd, false, HandleMenuMsg));
                 };