Fix target_server validation for service attachment (#14195) (#10181)

[upstream:a2335a05eb5feae5df981c54e94e9cca82ef0230]

Signed-off-by: Modular Magician <[email protected]>

Author: modular-magician

.changelog/14195.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+compute: fixed validation for `target_service`  in `google_compute_service_attachment`
+```

google-beta/services/compute/resource_compute_service_attachment.go

@@ -891,12 +891,13 @@ func expandComputeServiceAttachmentConnectionPreference(v interface{}, d tpgreso
 
 func expandComputeServiceAttachmentTargetService(v interface{}, d tpgresource.TerraformResourceData, config *transport_tpg.Config) (interface{}, error) {
 	resource := strings.Split(v.(string), "/")
-	resourceKind := resource[len(resource)-2]
-	resourceBound := resource[len(resource)-4]
 	if len(resource) < 4 {
 		return nil, fmt.Errorf("invalid value for target_service")
 	}
 
+	resourceKind := resource[len(resource)-2]
+	resourceBound := resource[len(resource)-4]
+
 	_, err := tpgresource.ParseRegionalFieldValue(resourceKind, v.(string), "project", resourceBound, "zone", d, config, true)
 	if err != nil {
 		return nil, fmt.Errorf("invalid value for target_service: %w", err)