interp: fix derivation of type of slice expression of binary object

Fixes #1328.

interp/type.go

@@ -854,6 +854,14 @@ func nodeType2(interp *Interpreter, sc *scope, n *node, seen []*node) (t *itype,
 		if err != nil {
 			return nil, err
 		}
+
+		if t.cat == valueT {
+			switch t.rtype.Kind() {
+			case reflect.Array, reflect.Ptr:
+				t = valueTOf(reflect.SliceOf(t.rtype.Elem()), withScope(sc))
+			}
+			break
+		}
 		if t.cat == ptrT {
 			t = t.val
 		}