Fix compatibility with libharu 2.4.0
Libharu 2.4.0 was recently released, and there are some breaking changes that require adjustments in
WPdfImage.h in order to get Wt to compile with version 2.4.0.
dash_ptnargument is now a
const HPDF_REAL*instead of
HPDF_PROJECTING_SCUARE_ENDwas changed to