Fixes crash #21896
Fixes crash #21896

Fix for a crash during terraform plan: If there is a multi-instance
resource (count > 1) where one of the instances was deleted in the
deployment but was still present in the terraform state,
getResourceInstancesAll crashed.

Check not only for rs.Instances[key] to exist, but also to have a
valid Current pointer.

hashicorp/terraform-plugin-sdk,hashicorp/terraform-plugin-sdk