storage: Fix error path in virStorageBackendSheepdogRefreshVol
storage: Fix error path in virStorageBackendSheepdogRefreshVol

If the virAsprintf of the vol->key fails, then we would erroneously
return the '0' from the @ret from virStorageBackendSheepdogParseVdiList.
So in this error path case, let's set ret = -1.

Signed-off-by: John Ferlan <87558058f6f829e5ec976c8ef960720af4ff9c7d@redhat.com>
Reviewed-by: Ján Tomko <4cab11cfb98d3c937327354a78eb07dbb6ee2bc6@redhat.com>

libvirt/libvirt,nertpinx/libvirt,libvirt/libvirt,nertpinx/libvirt,andreabolognani/libvirt,fabianfreyer/libvirt,jardasgit/libvirt,nertpinx/libvirt,libvirt/libvirt,eskultety/libvirt,crobinso/libvirt,crobinso/libvirt,zippy2/libvirt,nertpinx/libvirt,jardasgit/libvirt,crobinso/libvirt,andreabolognani/libvirt,eskultety/libvirt,eskultety/libvirt,jfehlig/libvirt,fabianfreyer/libvirt,fabianfreyer/libvirt,crobinso/libvirt,andreabolognani/libvirt,fabianfreyer/libvirt,andreabolognani/libvirt,olafhering/libvirt,zippy2/libvirt,eskultety/libvirt,jfehlig/libvirt,andreabolognani/libvirt,zippy2/libvirt,olafhering/libvirt,jfehlig/libvirt,jardasgit/libvirt,jardasgit/libvirt,nertpinx/libvirt,olafhering/libvirt,jfehlig/libvirt,libvirt/libvirt,jardasgit/libvirt,eskultety/libvirt,fabianfreyer/libvirt,zippy2/libvirt,olafhering/libvirt