provider/aws: ignore providers with Meta nil
provider/aws: ignore providers with Meta nil

We changed the way validation works for providers so that they aren't
always configured if they have computed attributes. The result is that
sometimes the Configure won't be called, hence Meta is nil

Ninir/terraform-provider-aws,ClementCunin/terraform-provider-aws,ClementCunin/terraform-provider-aws,nbaztec/terraform-provider-aws,charles-at-geospock/terraform-provider-aws,nbaztec/terraform-provider-aws,charles-at-geospock/terraform-provider-aws,kjmkznr/terraform-provider-aws,terraform-providers/terraform-provider-aws,ashinohara/terraform-provider-aws,terraform-providers/terraform-provider-aws,kjmkznr/terraform-provider-aws,Ninir/terraform-provider-aws,ClementCunin/terraform-provider-aws,kjmkznr/terraform-provider-aws,charles-at-geospock/terraform-provider-aws,Ninir/terraform-provider-aws,ashinohara/terraform-provider-aws,terraform-providers/terraform-provider-aws,Ninir/terraform-provider-aws,nbaztec/terraform-provider-aws,kjmkznr/terraform-provider-aws,charles-at-geospock/terraform-provider-aws,nbaztec/terraform-provider-aws,ClementCunin/terraform-provider-aws,ashinohara/terraform-provider-aws,terraform-providers/terraform-provider-aws,ashinohara/terraform-provider-aws