fix crashing whereby we can reach render loop when visual lines is not valid.
fix crashing whereby we can reach render loop when visual lines is not valid.


AvaloniaUI/AvaloniaEdit,AvaloniaUI/AvaloniaEdit,AvaloniaUI/AvaloniaEdit,danwalmsley/AvaloniaEdit,AvaloniaUI/AvaloniaEdit,AvaloniaUI/AvaloniaEdit,AvaloniaUI/AvaloniaEdit,AvaloniaUI/AvaloniaEdit,AvaloniaUI/AvaloniaEdit,AvaloniaUI/AvaloniaEdit,AvaloniaUI/AvaloniaEdit,AvaloniaUI/AvaloniaEdit,danwalmsley/AvaloniaEdit,AvaloniaUI/AvaloniaEdit,AvaloniaUI/AvaloniaEdit,AvaloniaUI/AvaloniaEdit,AvaloniaUI/AvaloniaEdit