fix: #2203 empty navitems break toc filter (#2204)
fix: #2203 empty navitems break toc filter (#2204)

* fix: #2203 empty navitems break toc filter

* fix: #2203 empty navitems break toc filter

* fix: #2203 empty navitems break toc filter

pascalberger/docfx,pascalberger/docfx,superyyrrzz/docfx,dotnet/docfx,superyyrrzz/docfx,pascalberger/docfx,dotnet/docfx,dotnet/docfx,superyyrrzz/docfx