Fix vds allocation

with `vds := make([]volumeDescriptor, 2)` we have
slice with two nil values, to which we later
append `vds = append(vds, vd)`, so PVD ends up to be
third element with svds appended after it.

Specs said there could be up to 127 SVDs, so,
let's allocate 0 elements with capacity 128: PVD + 127 SVDs.

Author: aol-nnov

filesystem/iso9660/iso9660.go

@@ -160,7 +160,7 @@ func Read(b backend.Storage, size, start, blocksize int64) (*FileSystem, error)
 	// we do not do anything with the system area for now
 
 	// next read the volume descriptors, one at a time, until we hit the terminator
-	vds := make([]volumeDescriptor, 2)
+	vds := make([]volumeDescriptor, 0, 128)
 	terminated := false
 	var (
 		pvd *primaryVolumeDescriptor