ppd-cache.c: Check for required attributes if URF or PWG Raster are found

ppd-cache.c: Check for required attributes if URF or PWG Raster are found

Some devices have image/urf in document-format-supported, but is missing urf-supported
if AirPrint support is turned off, which breaks PPD generation. Check for attribute
urf-supported when we are about to decide whether the printer uses AirPrint, so in case
the device supports another driverless standard, we can use it for PPD generation.
Apply the same for PWG Raster too.

Fixes Fedora issue #2263053