Made IMGUI_DISABLE_OBSOLETE_FUNCTIONS exceptionally not affect the layout of ImGuiIO. (#1695)

imgui.h

@@ -1043,9 +1043,12 @@ struct ImGuiIO
     void*       ImeWindowHandle;            // (Windows) Set this to your HWND to get automatic IME cursor positioning.
 
 #ifndef IMGUI_DISABLE_OBSOLETE_FUNCTIONS
-    // [OBSOLETE] Rendering function, will be automatically called in Render(). Please call your rendering function yourself now! You can obtain the ImDrawData* by calling ImGui::GetDrawData() after Render().
-    // See example applications if you are unsure of how to implement this.
+    // [OBSOLETE] Rendering function, will be automatically called in Render(). Please call your rendering function yourself now! 
+    // You can obtain the ImDrawData* by calling ImGui::GetDrawData() after Render(). See example applications if you are unsure of how to implement this.
     void        (*RenderDrawListsFn)(ImDrawData* data);
+#else
+    // This is only here to keep ImGuiIO the same size, so that IMGUI_DISABLE_OBSOLETE_FUNCTIONS can exceptionally be used outside of imconfig.h.
+    void*       RenderDrawListsFnDummy;
 #endif
 
     //------------------------------------------------------------------