ffmpeg: fix deinterlace

Fixes ticket1295
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

ffmpeg.c

@@ -2896,7 +2896,7 @@ static int init_input_stream(int ist_index, char *error, int error_len)
             return AVERROR(EINVAL);
         }
 
-        ist->dr1 = codec->capabilities & CODEC_CAP_DR1;
+        ist->dr1 = (codec->capabilities & CODEC_CAP_DR1) && !do_deinterlace;
         if (codec->type == AVMEDIA_TYPE_VIDEO && ist->dr1) {
             ist->st->codec->get_buffer     = codec_get_buffer;
             ist->st->codec->release_buffer = codec_release_buffer;