tpl/collections: Fix slice type handling in sort

The `sort` template func was producing a `[]page.Page` which did not work in `.Paginate`.

Fixes #6023

tpl/collections/sort.go

@@ -31,21 +31,23 @@ func (ns *Namespace) Sort(seq interface{}, args ...interface{}) (interface{}, er
 		return nil, errors.New("sequence must be provided")
 	}
 
-	seqv := reflect.ValueOf(seq)
-	seqv, isNil := indirect(seqv)
+	seqv, isNil := indirect(reflect.ValueOf(seq))
 	if isNil {
 		return nil, errors.New("can't iterate over a nil value")
 	}
 
+	var sliceType reflect.Type
 	switch seqv.Kind() {
-	case reflect.Array, reflect.Slice, reflect.Map:
-		// ok
+	case reflect.Array, reflect.Slice:
+		sliceType = seqv.Type()
+	case reflect.Map:
+		sliceType = reflect.SliceOf(seqv.Type().Elem())
 	default:
 		return nil, errors.New("can't sort " + reflect.ValueOf(seq).Type().String())
 	}
 
 	// Create a list of pairs that will be used to do the sort
-	p := pairList{SortAsc: true, SliceType: reflect.SliceOf(seqv.Type().Elem())}
+	p := pairList{SortAsc: true, SliceType: sliceType}
 	p.Pairs = make([]pair, seqv.Len())
 
 	var sortByField string