libcupsfilters: In pdftops() identify old LaserJets more precisely

libcupsfilters: In pdftops() identify old LaserJets more precisely

Old HP LaserJet printers have a firmware bug which makes them not
working with Ghostscript's PostScript output, so in pdftops() we
switch to Poppler for them.

We consider an old LaserJet every "HP LaserJet XXXXY" printer with
XXXX being a number (not preceded by a letter), typically 1-4 digits
and Y being 0-2 letters, no separated from the numbers by a space.

Unfortunately, we checked only whether after "LaserJet" comes a number
and not the rest. This made also modern printers with names like "HP
LaserJet 500 color M551" considered old and these modern printers have
another PostScript interpreter bug which makes them not print some
files with Poppler, so they need Ghostscript's PostScript output.

Therefore we refine the check for the old-LaserJet quirk to see
whether after the number are extra words and if so, this is again a
modern printer and we do not switch to Poppler.

See https://bugs.launchpad.net/bugs/1967816