Ensure region is set in ec2_vpc_subnet_facts (#30399)

Make requested change in #30370

lib/ansible/modules/cloud/amazon/ec2_vpc_subnet_facts.py

@@ -235,10 +235,13 @@ def main():
 
     region, ec2_url, aws_connect_params = get_aws_connection_info(module, boto3=True)
 
+    if region:
         try:
             connection = boto3_conn(module, conn_type='client', resource='ec2', region=region, endpoint=ec2_url, **aws_connect_params)
         except (botocore.exceptions.NoCredentialsError, botocore.exceptions.ProfileNotFound) as e:
             module.fail_json(msg=e.message, exception=traceback.format_exc(), **camel_dict_to_snake_dict(e.response))
+    else:
+        module.fail_json(msg="Region must be specified")
 
     describe_subnets(connection, module)