Wrong value for og:image when using path relative to protocol

For the project I'm working on, we are using path relative to the protocol instead of site document root for example :
<img src="//www.mydomain.com/sites/default/files/public/img_001.jpg" />

This create 2 problems with the module :
- on node's edit form, module is unable to display valid thumbnails
- on front office, meta tag "og:image" is set to a wrong URL : http://www.mydomain.com/www.mydomain.com/sites/default/files/public/img_001.jpg

To fix both points, I wrote the following patch that remove ltrim's usage and sets url as external.