Add new decoder property max_lowres and do not init decoder if requested value is higher.

Originally committed as revision 24098 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/h261dec.c

@@ -651,5 +651,6 @@ AVCodec h261_decoder = {
     h261_decode_end,
     h261_decode_frame,
     CODEC_CAP_DR1,
+    .max_lowres = 3,
     .long_name = NULL_IF_CONFIG_SMALL("H.261"),
 };