distribution: registry: do not access the errors slice if it's empty

[runcom]

Fix #21027
Regression from 1.9 which just prompt for user/pass on 401
See the discussion in the issue for more information

Signed-off-by: Antonio Murdaca runcom@redhat.com

[runcom]

ping @tiborvass @thaJeztah @Soulou

[tiborvass]

LGTM

[thaJeztah]

LGTM

[thaJeztah]

Thanks so much for the quick turnaround @runcom

[runcom]

tests pass but jobs always end with something like this:

15:41:39 Failed to remove container (docker-pr-userns7100): Error response from daemon: No such container: docker-pr-userns7100

[tiborvass]

@runcom yes its a CI issue, i'm investigating.

[tiborvass]

We don't care about experimental since this is a release.

[tiborvass]

Janky also passed, except for that stupid tar --include bug.
Gccgo is the only one that's actually failing...

[runcom]

gccgo tests don't fail: 16:25:58 OK: 1123 passed, 87 skipped

[tiborvass]

@runcom you're right I can't read. ok then we're good.

[Soulou]

Great, thanks @runcom for acting quickly!

[aaronlehmann]

Kind of surprised this doesn't also affect earlier versions: https://github.com/docker/docker/blob/v1.9.1/registry/registry.go#L215

Anyway, nice work with the quick fix.

[runcom]

@aaronlehmann acutally in 1.9, if the registry reply with 401 it will prompt for user/pass (which is not happening anymore in 1.10.x see #19159)

[ekristen]

Much appreciated! Thanks for the quick fix!