Initialize AuthConfigs map if it's nil before returning it.
This fixes fileStore.Store nil dereference panic when adding a new key
to the map.
Signed-off-by: Danial Gharib <danial.mail.gh@gmail.com>
Signed-off-by: Paweł Gronowski <pawel.gronowski@docker.com>
(cherry picked from commit ad43df5e86)
Signed-off-by: Paweł Gronowski <pawel.gronowski@docker.com>