`Selector.all` does not fail if any descendants match the given selectors

To reproduce:

```
Html.fieldset [ Attributes.disabled False ]
[ Html.button [ Attributes.disabled True ]
[ Html.text "Reply"
]
]
|> Query.fromHtml
|> Query.has
[ Selector.all
[ Selector.tag "fieldset"
, Selector.attribute (Attributes.disabled True)
]
]
```

Another example with a `class` selector:

```
Html.fieldset []
[ Html.button [ Attributes.class "btn btn-large" ]
[ Html.text "Reply"
]
]
|> Query.fromHtml
|> Query.has
[ Selector.all
[ Selector.tag "fieldset"
, Selector.class "btn"
]
]
```

Link to running examples: https://ellie-app.com/m7RYfvvLvjPa1

Actual result: it passes (because there is a descendant that matches the second selector)

Expected result: my understanding is that `Selector.all` allows us to find a single HTML element that matches all given selectors - if this is not the case, then I would say the description of this function should be clarified