libppd: In ppdFilterLoadPPD() let PDF filter log pages when output is PS

libppd: In ppdFilterLoadPPD() let PDF filter log pages when output is PS

PostScript output is going through the ppdFilterPSToPS() filter to
insert the PostScript code of the option settings into the PostScript
output data stream. The ppdFilterPSToPS() filter only logs pages if
the PPD is a pure PostScript PPD (without "*cupsFilter(2): ..."
lines). If it is not, the PDF filter has to log. This change lets the
PDF filter log the pages in such a case.