erp5_maileva_connector: Ensure it we dont have duplicated connectors

bt5/erp5_maileva_connector/SkinTemplateItem/portal_skins/erp5_maileva_connector/ERP5Site_getAvailableMailevaSOAPConnector.py

-maileva_connector = context.portal_catalog.getResultValue(
+maileva_connector_list = context.portal_catalog(
   portal_type='Maileva SOAP Connector',
-  reference=reference,
-  validation_state='validated')
-if not maileva_connector:
-  raise ValueError('Maileav soap connector is not defined')
-return maileva_connector
+  validation_state='validated',
+  limit=2)
+
+# Ensure there is no duplication.
+if not len(maileva_connector_list):
+  raise ValueError('Maileva soap connector is not defined')
+elif len(maileva_connector_list) != 1:
+  raise ValueError('More them one Maileva soap connector was found!')
+
+return maileva_connector_list[0]