Ensure VendorProduct uniqueness test is for new products only

Update Error message on duplicate - feedback from ops.

vince/models.py

@@ -3886,8 +3886,9 @@ class Meta:
         unique_together = (('name', 'organization'),)
 
     def save(self, *args, **kwargs):
-        if VendorProduct.objects.filter(organization=self.organization,
-                                        name__iexact=self.name):
+        dup = VendorProduct.objects.filter(organization=self.organization,
+                                           name__iexact=self.name)
+        if self._state.adding and dup:
             logger.debug(f"Ignoring duplicate VendorProduct {self.name}")
             return
         return super(VendorProduct, self).save(*args, **kwargs)

vince/views.py

@@ -9758,8 +9758,9 @@ def post(self, request, *args, **kwargs):
         sectors = self.request.POST.getlist('sector')
 
         if VendorProduct.objects.filter(organization=contact,name__iexact=name):
-            messages.error(self.request,_("Duplicate product names not allowed"))
-            return HttpResponseRedirect(reverse('vince:contact', args=[self.kwargs["pk"]]))
+            messages.error(self.request,_("Product (case insensitive) and Vendor tuple shoud be unique!"))
+            return HttpResponseRedirect(reverse('vince:contact', args=[self.kwargs["pk"]]) + '#products')            
+
 
         product = VendorProduct(name=name,
                     sector=sectors,