Fix initialization bug in FakeImageService

When adding this functionality in
https://github.com/kubernetes/kubernetes/pull/88372, I forgot to
allocate a map for the `Errors` field when constructing the object. As a
result, trying to actually use the `InjectError` method failed (as I
noticed when I started trying to write tests to actually use
`InjectError`). Fortunately, `FakeImageService` is only used in tests...
but still, we should fix this issue.

Fixing in a separate diff from the one which will add additional test
coverage (and actually use `InjectError`, because I don't like having
non-working code in master.)

We could also revert the original commit and then re-merge with this
fix, but that seems like unnecessary work given we already have a fix
ready to go.

staging/src/k8s.io/cri-api/pkg/apis/testing/fake_image_service.go

@@ -65,6 +65,7 @@ func (r *FakeImageService) SetFakeFilesystemUsage(usage []*runtimeapi.Filesystem
 func NewFakeImageService() *FakeImageService {
 	return &FakeImageService{
 		Called: make([]string, 0),
+		Errors: make(map[string][]error),
 		Images: make(map[string]*runtimeapi.Image),
 	}
 }