libppd: In ppdFilterUniversal() set output data type also if no PPD supplied

libppd: In ppdFilterUniversal() set output data type also if no PPD supplied

Now both cfFilterUniversal() and its PPD file support wrapper
ppdFilterUniversal() are absolutely compatible if no PPD file got
supplied via named extension to the filter data.

Before, if no PPD was supplied and no actual_output_type in the
parameters, the output data type stayed undetermined and the function
errored out not being able to find a filter combination for the
requested conversion.

Now always final_content_type of thef ilter data is used if there is
no actual_output_type specified in the parameters, regardless of
whether we have a PPD file or not.