Less confused about `max() + calc()`

```
$ lessc --version
lessc 4.1.1 (Less Compiler) [JavaScript]
$ lessc  <(echo 'body { padding: max(1em, calc(50vw - 25rem)); } ')
body {
  padding: 1em;
}
```

Expected output:

```
body {
  padding: max(1em, calc(50vw - 25rem));
}
```

Any subset of the expression (e.g. `max(1em, 50vw)` or `calc(50vw -
25rem)`) works fine.
