Autoloader doesn't load data-dependencies of elements with already loaded languages

[RunDevelopment]

Information:

• Prism version: 1.16
• Environment: Browser

Description
Autoloader will ignore the data-dependencies of elements if the language of the element is loaded already.

Suppose we have already loaded the JavaScript language. If we then want to highlight this element:

<pre data-dependencies="js-extras"><code class="language-javascript">
    console.log("foo");
</code></pre>

Then Autoloader will do nothing. JS Extras will not be loaded.

Example
An example of this can be seen in #1936 on the examples page. Open the examples page, select JavaScript, select JS Extras, and see that JS Extras wasn't loaded.