DrawList: fixed CloneOutput() taking a copy of the ImDrawListSharedData pointer. (#8894, #1860)

Amend b82e99c032

imgui.h

@@ -3316,7 +3316,7 @@ struct ImDrawList
 
     // Advanced: Miscellaneous
     IMGUI_API void  AddDrawCmd();                                               // This is useful if you need to forcefully create a new draw call (to allow for dependent rendering / blending). Otherwise primitives are merged into the same draw-call as much as possible
-    IMGUI_API ImDrawList* CloneOutput() const;                                  // Create a clone of the CmdBuffer/IdxBuffer/VtxBuffer.
+    IMGUI_API ImDrawList* CloneOutput() const;                                  // Create a clone of the CmdBuffer/IdxBuffer/VtxBuffer. For multi-threaded rendering, consider using `imgui_threaded_rendering` from https://github.com/ocornut/imgui_club instead.
 
     // Advanced: Channels
     // - Use to split render into layers. By switching channels to can render out-of-order (e.g. submit FG primitives before BG primitives)

imgui_draw.cpp

@@ -478,9 +478,10 @@ void ImDrawList::_ClearFreeMemory()
     _Splitter.ClearFreeMemory();
 }
 
+// Note: For multi-threaded rendering, consider using `imgui_threaded_rendering` from https://github.com/ocornut/imgui_club
 ImDrawList* ImDrawList::CloneOutput() const
 {
-    ImDrawList* dst = IM_NEW(ImDrawList(_Data));
+    ImDrawList* dst = IM_NEW(ImDrawList(NULL));
     dst->CmdBuffer = CmdBuffer;
     dst->IdxBuffer = IdxBuffer;
     dst->VtxBuffer = VtxBuffer;