Backport (7.8) - Regression: External links are opened in Template Composer

To reproduce (using Go Green):
1. Go to the Channel Manager and open the English channel in the CMS
2. Click Products, then Fennel
3. Click one of the links at the bottom
Expected result: The link should not be opened
Actual result: The external site opens in the Channel Manager. Clicking "Edit Channel" will make the client hang.

See CMS7-5647.