slapos_cloud: no need to search a Software Product if there is no url_string

master/bt5/slapos_cloud/SkinTemplateItem/portal_skins/slapos_cloud/InstanceTree_getSoftwareProduct.py

@@ -4,15 +4,17 @@ software_product = None
 software_release = None
 software_type = None
 
-use_category_uid = portal.restrictedTraverse("portal_categories/use/trade/sale").getUid(),
-product_list = portal.portal_catalog(
+if url_string:
+
+  use_category_uid = portal.restrictedTraverse("portal_categories/use/trade/sale").getUid(),
+  product_list = portal.portal_catalog(
     portal_type="Software Product",
     validation_state=['validated', 'published'],
     use__uid=use_category_uid,
     follow_up__uid=context.getFollowUpUid()
-)
+  )
 
-if len(product_list) != 0:
+  if len(product_list) != 0:
     software_release = portal.portal_catalog.getResultValue(
       portal_type="Software Product Release Variation",
       url_string=url_string,