Fix errors 500 shown in Modeler when using an account with an email address for login

• Log in to NOS using a trial account: your username will have an email address.
• Go to Studio Designer
• Open console

=> Plenty of errors 500 show up, all related to the same code line

Expected: no error 500 should show up

Note: in Modeler, error in shown only once and comes from nuxeo-studio-elements.html => seems related to the initials we are trying to show in the user menu button (they don't show up) but that's only an hypothesis.