If we encounter a provider with old inputs but no old outputs when reading
a checkpoint file, use the old inputs as the old outputs. This handles the
scenario where the CLI is being upgraded from a version that did not
reflect provider inputs to provider outputs, and a provider is being
upgraded from a version that did not implement `DiffConfig` to a version
that does.
Fixes https://github.com/pulumi/pulumi-kubernetes/issues/645.
fa05e5cb05