server: fix segfault on cleanup
server: fix segfault on cleanup

don't try to access the infra container if it is not set.

github.com/kubernetes-sigs/cri-o/oci.(*Runtime).ContainerStatus(0xc000420300, 0x0, 0x0)
	/gopath/src/github.com/kubernetes-sigs/cri-o/oci/oci.go:895 +0x2f
github.com/kubernetes-sigs/cri-o/server.(*Server).stopPodSandbox(0xc000324000, 0x1ae2f60, 0xc0001bef60, 0xc0002800e0, 0x0, 0x0, 0x0)
	/gopath/src/github.com/kubernetes-sigs/cri-o/server/sandbox_stop_linux.go:57 +0x1ff
github.com/kubernetes-sigs/cri-o/server.(*Server).StopPodSandbox(0xc000324000, 0x1ae2f60, 0xc0001bef60, 0xc0002800e0, 0x2, 0x2, 0x1abf340)
	/gopath/src/github.com/kubernetes-sigs/cri-o/server/sandbox_stop.go:13 +0x49
github.com/kubernetes-sigs/cri-o/server.(*Server).runPodSandbox(0xc000324000, 0x1ae2f60, 0xc0001bef60, 0xc000351cc0, 0x0, 0x1abf340, 0xc0002800d0)
	/gopath/src/github.com/kubernetes-sigs/cri-o/server/sandbox_run_linux.go:67 +0x9194
github.com/kubernetes-sigs/cri-o/server.(*Server).RunPodSandbox(0xc000324000, 0x1ae2f60, 0xc0001bef60, 0xc000351cc0, 0xc000324000, 0xf8, 0xc000215b50)
	/gopath/src/github.com/kubernetes-sigs/cri-o/server/sandbox_run.go:130 +0x49
github.com/kubernetes-sigs/cri-o/vendor/k8s.io/kubernetes/pkg/kubelet/apis/cri/runtime/v1alpha2._RuntimeService_RunPodSandbox_Handler(0x18b9900, 0xc000324000, 0x1ae2f60, 0xc0001bef60, 0xc0002d47d0, 0x0, 0x0, 0x0, 0x18c3501, 0x9)

Signed-off-by: Giuseppe Scrivano <20002b7b24c75512093a71a58285826d5c504fca@redhat.com>

mikebrow/cri-o,kubernetes-incubator/ocid,rhatdan/cri-o,nalind/cri-o,kubernetes-incubator/ocid,kubernetes-incubator/cri-o,nalind/cri-o,kubernetes-incubator/ocid,mikebrow/cri-o,kubernetes-incubator/cri-o,nalind/cri-o,rhatdan/cri-o,kubernetes-incubator/cri-o,mikebrow/cri-o,rhatdan/cri-o,mikebrow/cri-o,kubernetes-incubator/cri-o,rhatdan/cri-o