tpl: Last now accepts 0 as limit

Modified the if conditional because of which last threw an error if 0 was passed as limit. The function now returns an empty slice if it is called with 0 as limit. The behavior of first and last is now the same when 0 is passed as limit. Also added tests to test the new behavior.

Fixes #6419

tpl/collections/collections.go

@@ -378,7 +378,7 @@ func (ns *Namespace) Last(limit interface{}, seq interface{}) (interface{}, erro
 		return nil, err
 	}
 
-	if limitv < 1 {
+	if limitv < 0 {
 		return nil, errors.New("can't return negative/empty count of items from sequence")
 	}