implicitclass: If IPP poll of printer fails, use PPD file for capabilities

implicitclass: If IPP poll of printer fails, use PPD file for capabilities

Member printers of a cups-browsed printer cluster are always IPP
printers, in most cases driverless IPP (IPP 2.x) printers and here a
get-printer-attributes IPP request gets all needed capability info
from the destination printer in order to run the filters to turn the
PDF input into the printer's data format.

If the destination printer is a legacy IPP (IPP 1.x) printer, our
get-printer-attributes IPP request fails (we accept only IPP 2.x here)
and then we fall back to using the PPD file. The PPD file is the
cluster's PPD, not the printer's, but all settings are supported by
our destination printer (otherwise it would not have gotten selected).

This way we recover support for legacy IPP printers which got dropped
with the recent commits to switch over to use filter functions instead
of external filter executables.