New PR: Fixed PHP Warning

New Fix for https://github.com/joomla/joomla-cms/pull/4070

### How to test
First point that need tested
1. pass to parse_url() a bad url, for example: JString::parse_url('http:///www.mysite.com/dir');
Seccond:
1. Set Use Unicode  Alias to Yes in Global Configuration
2. Pick up or make for example a single article menu item (not Home) and change/create its alias to contain unicode (Example: moç-contøct)
3. Click on the menu item before and after patch.
4. Bevor and after the patch you will get the same page without error.

thanks @demis-palma and @infograf768

### Tracker
http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=34040&start=0