Bug#1042165: pdf-presenter-console: FTBFS: drawing_commands.vala:57.46-57.59: error: `pdfpc.DrawingCommand' is not a supported generic type argument, use `?' to box value types

[Evgeny Stambulchik]

Fix in the upstream:

<https://github.com/pdfpc/pdfpc/pull/687/files>