avformat/segafilm - revert keyframe detection

Keyframe detection was inverted in cfe1a9d311 in order to fix keyframe
flags set for the sample attached to trac #7091. However, that sample is
errantly muxed.

As noted at
https://web.archive.org/web/20020803104640/http://www.pcisys.net:80/~melanson/codecs/film-format.txt,
the original keyframe detection logic is correct, and this patch
restores it.

Signed-off-by: James Almer <jamrial@gmail.com>

libavformat/segafilm.c

@@ -239,7 +239,7 @@ static int film_read_header(AVFormatContext *s)
         } else {
             film->sample_table[i].stream = film->video_stream_index;
             film->sample_table[i].pts = AV_RB32(&scratch[8]) & 0x7FFFFFFF;
-            film->sample_table[i].keyframe = (scratch[8] & 0x80) ? AVINDEX_KEYFRAME : 0;
+            film->sample_table[i].keyframe = (scratch[8] & 0x80) ? 0 : AVINDEX_KEYFRAME;
             video_frame_counter++;
             if (film->video_type)
                 av_add_index_entry(s->streams[film->video_stream_index],