ffmpeg: fix setting codecs for demuxers.

Bug introduced by:
commit e3bf4e29
Author: Anton Khirnov <anton@khirnov.net>
Date:   Tue Aug 30 04:10:54 2011 +0200

    ffmpeg: replace -vcodec/-acodec/-scodec with a better system.

    The new option doesn't depend on its placement wrt -new* options (which
    don't exist anymore) and works in a similar way as per-stream AVOptions.

    -[vas]codec remain as aliases to -codec:[vas]
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

ffmpeg.c

@@ -3118,6 +3118,12 @@ static int opt_input_file(OptionsContext *o, const char *opt, const char *filena
     if (o->nb_frame_pix_fmts)
         av_dict_set(&format_opts, "pixel_format", o->frame_pix_fmts[o->nb_frame_pix_fmts - 1].u.str, 0);
 
+    ic->video_codec_id   =
+        find_codec_or_die(video_codec_name   , AVMEDIA_TYPE_VIDEO   , 0);
+    ic->audio_codec_id   =
+        find_codec_or_die(audio_codec_name   , AVMEDIA_TYPE_AUDIO   , 0);
+    ic->subtitle_codec_id=
+        find_codec_or_die(subtitle_codec_name, AVMEDIA_TYPE_SUBTITLE, 0);
     ic->flags |= AVFMT_FLAG_NONBLOCK;
 
     if (loop_input) {