Effects: Don't overwrite display:none when .hide()ing hidden elements

Fixes [#14848](http://bugs.jquery.com/ticket/14848)

```
   raw     gz Sizes
246357  72980 dist/jquery.js
 84041  29395 dist/jquery.min.js

   raw     gz Compared to master @ a10aa3aac5223c250327d00c500ceb9c7a18b7f9
  +290    +87 dist/jquery.js
   +70    +18 dist/jquery.min.js
```