Fixed a situation where CTRL+Tab or Modal can occasionally lead to the creation of ImDrawCmd with zero triangles, (#4857)

(2nd amend)

Author: ocornut

docs/CHANGELOG.txt

@@ -46,6 +46,8 @@ Breaking Changes:
 
 Other Changes:
 
+- Fixed a situation where CTRL+Tab or Modal can occasionally lead to the creation of ImDrawCmd with zero triangles,
+  which would makes the draw operation of some backends assert (e.g. Metal with debugging). (#4857)
 - Tables, ImDrawListSplitter: Fixed erroneously stripping trailing ImDrawList::AddCallback() when submitted in
   last column or last channel and when there are no other drawing operation. (#4843, #4844) [@hoffstadt]
 - Backends: OpenGL3: Fixed a buffer overflow in imgui_impl_opengl3_loader.h init (added in 1.86). (#4468, #4830) [@dymk]

imgui.cpp

@@ -4475,6 +4475,7 @@ static void ImGui::RenderDimmedBackgroundBehindWindow(ImGuiWindow* window, ImU32
         draw_list->CmdBuffer.pop_back();
         draw_list->CmdBuffer.push_front(cmd);
         draw_list->PopClipRect();
+        draw_list->_PopUnusedDrawCmd(); // Since are past the calls to AddDrawListToDrawData() we don't have a _PopUnusedDrawCmd() running on commands.
     }
 }
 
@@ -4528,6 +4529,7 @@ static void ImGui::RenderDimmedBackgrounds()
         window->DrawList->PushClipRect(viewport->Pos, viewport->Pos + viewport->Size);
         window->DrawList->AddRect(bb.Min, bb.Max, GetColorU32(ImGuiCol_NavWindowingHighlight, g.NavWindowingHighlightAlpha), window->WindowRounding, 0, 3.0f);
         window->DrawList->PopClipRect();
+        window->DrawList->_PopUnusedDrawCmd(); // Since are past the calls to AddDrawListToDrawData() we don't have a _PopUnusedDrawCmd() running on commands.
     }
 }