pci: don't pass chroot to pcidb with snapshots

Snapshot implementation leverages chroot and transparently set it
to the unpacked snapshot root. This is the intentional behaviour
and ghw supports it.
But the `pci` package passes throu the chroot settings to `pcidb`
and the latter doesn't know or care about ghw snapshots - and rightly
so!

hence, we need to pass through the `chroot` setting only if explicitely
set by client code - so if no snapshot settings are present.

Signed-off-by: Francesco Romani <fromani@redhat.com>

pkg/pci/pci_linux.go

@@ -15,13 +15,27 @@ import (
 
 	"github.com/jaypipes/ghw/pkg/context"
 	"github.com/jaypipes/ghw/pkg/linuxpath"
+	"github.com/jaypipes/ghw/pkg/option"
 	pciaddr "github.com/jaypipes/ghw/pkg/pci/address"
 	"github.com/jaypipes/ghw/pkg/topology"
 	"github.com/jaypipes/ghw/pkg/util"
 )
 
 func (i *Info) load() error {
-	db, err := pcidb.New(pcidb.WithChroot(i.ctx.Chroot))
+	// when consuming snapshots - most notably, but not only, in tests,
+	// the context pkg forces the chroot value to the unpacked snapshot root.
+	// This is intentional, intentionally transparent and ghw is prepared to handle this case.
+	// However, `pcidb` is not. It doesn't know about ghw snaphots, nor it should.
+	// so we need to complicate things a bit. If the user explicitely supplied
+	// a chroot option, then we should honor it all across the stack, and passing down
+	// the chroot to pcidb is the right thing to do. If, however, the chroot was
+	// implcitely set by snapshot support, then this must be consumed by ghw only.
+	// In this case we should NOT pass it down to pcidb.
+	chroot := i.ctx.Chroot
+	if i.ctx.SnapshotPath != "" {
+		chroot = option.DefaultChroot
+	}
+	db, err := pcidb.New(pcidb.WithChroot(chroot))
 	if err != nil {
 		return err
 	}