Check path in method hasFile.

This pull-request solves a problem encountered when uploading a "corrupt" file like one of the files you can found at <a href="http://www.thinkbroadband.com/download.html">Thinkbroad</a>.

Any of these files is considered empty in the validation (I am checking that a image is uploaded), therefore these pass validation. However, in the controller, when I try to save the image I check if Input has the file and this returned true.

This commit solves this problem. Previously a corrupt file passed the validation because is considered empty and is not required, but was not considered empty by the method Input::hasFile().