BeginMenu(): Menus: Fixed a one-frame issue where SetNextWindowXXX data are not consumed by a BeginMenu().

+ Shallow tweaks to reduce diff of future branches. Removing early return also facilitate some changes.

imgui_demo.cpp

@@ -1084,6 +1084,7 @@ static void ShowDemoWindowWidgets()
     IMGUI_DEMO_MARKER("Widgets/Combo");
     if (ImGui::TreeNode("Combo"))
     {
+        // Combo Boxes are also called "Dropdown" in other systems
         // Expose flags as checkbox for the demo
         static ImGuiComboFlags flags = 0;
         ImGui::CheckboxFlags("ImGuiComboFlags_PopupAlignLeft", &flags, ImGuiComboFlags_PopupAlignLeft);