aws: Let acc ID validation fail when we have no ID

- we could've had ConflictsWith between affected fields, but that would make it fail even if skip_requesting_account_id=false and ConflictsWhen is not a thing (yet)

builtin/providers/aws/config.go

@@ -217,12 +217,12 @@ func (c *Config) Client() (interface{}, error) {
 			if err == nil {
 				client.accountid = accountId
 			}
+		}
 
 		authErr := c.ValidateAccountId(client.accountid)
 		if authErr != nil {
 			errs = append(errs, authErr)
 		}
-		}
 
 		client.apigateway = apigateway.New(sess)
 		client.appautoscalingconn = applicationautoscaling.New(sess)