I think it makes sense. If Alias is empty, use username.
This helps because login are sometimes meaningless, and also it is good to keep login private.
I am not convinced it is wise to change this now, since Alias have been useless all this time, could be annoying to display random values (possibly wrong) in the top bar
(In ) Fixes #2192 I forgot users can update their own aliasin the settings so it is def better showing "Hello, $alias!"