af_comics filters: don't try to load empty html

plugins/af_comics/filters/af_comics_cad.php

plugins/af_comics/filters/af_comics_comicclass.php

plugins/af_comics/filters/af_comics_comicpress.php

plugins/af_comics/filters/af_comics_darklegacy.php

plugins/af_comics/filters/af_comics_dilbert.php

plugins/af_comics/filters/af_comics_pa.php

plugins/af_comics/filters/af_comics_pvp.php

plugins/af_comics/filters/af_comics_tfd.php

plugins/af_comics/filters/af_comics_twp.php

plugins/af_comics/filters/af_comics_whomp.php