libcupsfilters: In texttopdf() did redirrection of stdout to outputfd

libcupsfilters: In texttopdf() did redirrection of stdout to outputfd

The texttopdf() filter function was missing the redirection of stdout
to the output file descriptor of the function call, outputfd.

On error of parsing the charset configuration file and loading the
fonts exit(1) was called which would kill the caller in a filter
function. This is corrected now, too.