Double colon displayed in Forgot username mail content

Steps to reproduce

1. Click Log-in from the top right corner
2. Click 'Forgot your username?'
3. Fill in the email address which was set up in an existing user's profile
4. Click 'Retrieve username' button
5. Observe the email received by that user

Expected results

The email received has a single colon on the end of the following sentence:

 We found the following usernames related to this email address:

Actual results

There are 2 colons displayed at the end of the sentence (see also the screenshot).

 We found the following usernames related to this email address: :

Tested and reproduced also on XWiki 15.10.10 and 16.4.0.