oggenc aiff_open buffer overflow

I discovered an buffer overflow issue in oggenc/audio.c when it tries to open invalid aiff file.

274    if(fread(buffer,1,len,in) < len)

The 'len' here can be controlled by user indirectly via:

260    if(!find_aiff_chunk(in, "COMM", &len))

The attached aiff file can be used to reproduce this issue. I was testing with vorbis-tools-1.4.0