tpl: After now accepts 0 as index

Modified the if conditional because of which after threw an error if called with 0 as index. The function now returns the whole original slice if 0 is passed as an index. Also added tests to test the new behavior.

Fixes #6388

tpl/collections/collections.go

@@ -60,7 +60,7 @@ func (ns *Namespace) After(index interface{}, seq interface{}) (interface{}, err
 		return nil, err
 	}
 
-	if indexv < 1 {
+	if indexv < 0 {
 		return nil, errors.New("can't return negative/empty count of items from sequence")
 	}
 

tpl/collections/collections_test.go

@@ -50,6 +50,8 @@ func TestAfter(t *testing.T) {
 		{int64(2), []int{100, 200, 300}, []int{300}},
 		{100, []int{100, 200}, []int{}},
 		{"1", []int{100, 200, 300}, []int{200, 300}},
+		{0, []int{100, 200, 300, 400, 500}, []int{100, 200, 300, 400, 500}},
+		{0, []string{"a", "b", "c", "d", "e"}, []string{"a", "b", "c", "d", "e"}},
 		{int64(-1), []int{100, 200, 300}, false},
 		{"noint", []int{100, 200, 300}, false},
 		{2, []string{}, []string{}},