libppd: In ppdFilterLoadPPD() correct check for final output type

libppd: In ppdFilterLoadPPD() correct check for final output type

To determine whether the PDF filter (usually cfFilterPDFToPDF()) has
to do the page logging for CUPS ("PAGE: XX YY" log messages) or the
driver filter, we check the final output type (FINAL_CONTENT_TYPE
environment cariable from CUPS) to see whether a driver filter is
involved which should log the pages by itself.

The code to compare the final output type with the "*cupsFilter(2):
..." lines in the PPD file was broken, which is fixed with this
commit.