Do not crash on letter-spacing: normal
Do not crash on letter-spacing: normal

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