avcodec/fraps: use BT.709 colorspace for YUV Fraps versions

Based both on comparison to the reference decoder, and comments from
the fraps developers upon inquiry how to handle the yuv fraps variants.

libavcodec/fraps.c

@@ -206,6 +206,7 @@ static int decode_frame(AVCodecContext *avctx,
 
     avctx->pix_fmt = version & 1 ? AV_PIX_FMT_BGR24 : AV_PIX_FMT_YUVJ420P;
     avctx->color_range = version & 1 ? AVCOL_RANGE_UNSPECIFIED : AVCOL_RANGE_JPEG;
+    avctx->colorspace = version & 1 ? AVCOL_SPC_UNSPECIFIED : AVCOL_SPC_BT709;
 
     if ((ret = ff_thread_get_buffer(avctx, &frame, 0)) < 0)
         return ret;