erp5_configurator: prevent zerodivisionerror

After discussing on
!1103 (comment 104474) we
amended the original commit so that if there are no bt to install at
this point we consider this step is finished (use 1 and not 0)

bt5/erp5_configurator/SkinTemplateItem/portal_skins/erp5_configurator_wizard/ConfiguratorTool_viewRunningInstallationMessage.py

@@ -13,7 +13,10 @@ is_bt5_installation_running = installation_status['bt5']['all']!=0 and \
 if not is_bt5_building_running:
   all_bt5s = float(installation_status['bt5']['all'])
   current_bt5s = float(installation_status['bt5']['current'])
-  bt5_percent_of_total = current_bt5s / all_bt5s
+  if all_bt5s:
+    bt5_percent_of_total = current_bt5s / all_bt5s
+  else:
+    bt5_percent_of_total = 1
   calc_percentage = calc_percentage + building_bt5_part_percentage + \
                     bt5_percent_of_total*installation_bt5_part_percentage