Take positive values for last known staff (cgscop#37)

models/res_partner.py

@@ -684,12 +684,13 @@ class ScopPartner(models.Model):
             else:
                 partner.membership_status = "not_member"
 
-    @api.depends('questionnaire_ids')
+    @api.depends('questionnaire_ids', 'questionnaire_ids.staff_count',
+                 'questionnaire_ids.effective_date')
     @api.multi
     def _compute_last_effective(self):
         for partner in self:
-            lm = partner.questionnaire_ids.search([
-                ['partner_id', '=', partner.id]],
+            lm = partner.questionnaire_ids.search(
+                [['partner_id', '=', partner.id], ['staff_count', 'gt', 0]],
                 limit=1,
                 order='effective_date desc')
             if lm: