r/aws_elasticache_replication_group: fix crash setting replicas_per_node_group

[jar-b]

Description

In cases where the NodeGroups list in the read ouput is empty, the provider would crash attempting to read the NodeGroupMembers count from the first item in the list.

Relations

Closes #37771

Output from Acceptance Testing

% make testacc PKG=elasticache TESTS="TestAccElastiCacheReplicationGroup_basic|TestAccElastiCacheReplicationGroup_ClusterMode_basic"
make: Verifying source code with gofmt...
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go1.22.6 test ./internal/service/elasticache/... -v -count 1 -parallel 20 -run='TestAccElastiCacheReplicationGroup_basic|TestAccElastiCacheReplicationGroup_ClusterMode_basic'  -timeout 360m

--- PASS: TestAccElastiCacheReplicationGroup_basic_v5 (775.08s)
--- PASS: TestAccElastiCacheReplicationGroup_basic (775.23s)
--- PASS: TestAccElastiCacheReplicationGroup_ClusterMode_basic (915.76s)
PASS
ok      github.com/hashicorp/terraform-provider-aws/internal/service/elasticache        921.685s

[github-actions]

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[ewbankkit]

LGTM 🚀.

[github-actions]

This functionality has been released in v5.63.0 of the Terraform AWS Provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

For further feature requests or bug reports with this functionality, please create a new GitHub issue following the template. Thank you!

[github-actions]

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