Fix Request::hasFile with an array of files

This fixes the following error scenario:

```
<input type="file" name="images[image1]" />
<input type="file" name="images[image2]" />
```

Before, if image2 was uploaded but image1 wasn't, `Input::hasFile('images')` would return false even though an file was uploaded.
Please import `SplFileInfo` at the top of the file.