ImDrawData: call _PopUnusedDrawCmd() later. as RenderDimmedBackgrounds() rely on a valid command being there (especially in docking branch). (#6406, #4879, #1878)

Amend/fix dbeeeae for docking.
+ Build fix when using IMGUI_DISABLE_DEBUG_TOOLS

imgui.cpp

@@ -5356,8 +5356,12 @@ void ImGui::Render()
         if (viewport->DrawLists[1] != NULL)
             AddDrawListToDrawDataEx(&viewport->DrawDataP, viewport->DrawDataBuilder.Layers[0], GetForegroundDrawList(viewport));
 
+        // We call _PopUnusedDrawCmd() last thing, as RenderDimmedBackgrounds() rely on a valid command being there (especially in docking branch).
         ImDrawData* draw_data = &viewport->DrawDataP;
         IM_ASSERT(draw_data->CmdLists.Size == draw_data->CmdListsCount);
+        for (int draw_list_n = 0; draw_list_n < draw_data->CmdLists.Size; draw_list_n++)
+            draw_data->CmdLists[draw_list_n]->_PopUnusedDrawCmd();
+
         g.IO.MetricsRenderVertices += draw_data->TotalVtxCount;
         g.IO.MetricsRenderIndices += draw_data->TotalIdxCount;
     }

imgui_draw.cpp

@@ -1859,7 +1859,6 @@ void ImGui::AddDrawListToDrawDataEx(ImDrawData* draw_data, ImVector<ImDrawList*>
 
     // Add to output list + records state in ImDrawData
     out_list->push_back(draw_list);
-    draw_list->_PopUnusedDrawCmd();
     draw_data->CmdListsCount++;
     draw_data->TotalVtxCount += draw_list->VtxBuffer.Size;
     draw_data->TotalIdxCount += draw_list->IdxBuffer.Size;
@@ -1868,6 +1867,7 @@ void ImGui::AddDrawListToDrawDataEx(ImDrawData* draw_data, ImVector<ImDrawList*>
 void ImDrawData::AddDrawList(ImDrawList* draw_list)
 {
     IM_ASSERT(CmdLists.Size == CmdListsCount);
+    draw_list->_PopUnusedDrawCmd();
     ImGui::AddDrawListToDrawDataEx(this, &CmdLists, draw_list);
 }