Skip updating containers where no local image info can be retrieved

[piksel]

Partially reverts #571, since it causes dockerClient.StartContainer() to crash since it uses imageInfo to rebuild the config.

Fixes #584

[tammert]

Won't this reintroduce #215 though? In the situation where the running container uses an image that it not available locally (anymore).

[simskij]

@tammert

Won't this reintroduce #215 though? In the situation where the running container uses an image that it not available locally (anymore).

It might very well do that, however - it will still grab oldImageID from ContainerJSONBase, which I think is the crucial part of your previous fix, right?

What happens right now, is that all other calls to ImageInfo throughout the code will try to dereference a null pointer, and as a result, crashes watchtower. For instance:

https://github.com/containrrr/watchtower/blob/master/pkg/container/container.go#L166-L208

I think any suggestion as to how to do this differently is welcome, though, as relying on ImageInfo seems to be a fragile solution in general.

I'm holding off on approving this review until we've sorted out this discussion. 👍

[tammert]

LGTM 👍