Values >4 for lowres corrupt output.

Originally committed as revision 26386 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/mjpegdec.c

@@ -1547,7 +1547,7 @@ AVCodec mjpeg_decoder = {
     ff_mjpeg_decode_frame,
     CODEC_CAP_DR1,
     NULL,
-    .max_lowres = 8,
+    .max_lowres = 4,
     .long_name = NULL_IF_CONFIG_SMALL("MJPEG (Motion JPEG)"),
 };