blkdebug: pass getlength to underlying file This is required when using blkdebug with raw format. Unlike qcow2/QED, raw asks blkdebug for the length of the file, it doesn't get it from a header. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>