loader: cd9660_open() warn: is 'buf' large enough for 'struct iso_primary_descriptor'?

We do allocate amount of memory (void * or char *), and then assign this
buffer to struct iso_primary_descriptor *vd. Make sure we do
allocate enough bytes.

In fact we do allocate enough, but it is good idea to make sure this really
is so.

MFC after: 1 week