100l, fix missing decrement on split PGS packets.

Originally committed as revision 25810 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/pgssubdec.c

@@ -182,6 +182,7 @@ static int parse_picture_segment(AVCodecContext *avctx,
 
         memcpy(ctx->picture.rle + ctx->picture.rle_data_len, buf, buf_size);
         ctx->picture.rle_data_len += buf_size;
+        ctx->picture.rle_remaining_len -= buf_size;
 
         return 0;
     }