Allow PMT filters to be disabled even when config file is used.

Commit 77382fc5 enabled PMT filters when config file was used.

This commit allows PMT filters to be disabled by using --select-pmts (-w)
option after the config file is set.

Now running 'dvblast [opts] --config-file file.conf --select-pmts'
instructs dvblast to *NOT* set filters for all PMTs.