Work around a bug on content empty pages.
Work around a bug on content empty pages.

andrewleech/WeasyPrint,jasco/WeasyPrint,marclaporte/WeasyPrint,Kozea/WeasyPrint,jasco/WeasyPrint,Kozea/WeasyPrint,marclaporte/WeasyPrint,prepare/TestWeasyPrint,andrewleech/WeasyPrint,prepare/TestWeasyPrint