Allow space in username

Jellyfin.Server.Implementations/Users/UserManager.cs

@@ -767,7 +767,7 @@ namespace Jellyfin.Server.Implementations.Users
             // This is some regex that matches only on unicode "word" characters, as well as -, _ and @
             // In theory this will cut out most if not all 'control' characters which should help minimize any weirdness
             // Usernames can contain letters (a-z + whatever else unicode is cool with), numbers (0-9), at-signs (@), dashes (-), underscores (_), apostrophes ('), and periods (.)
-            return Regex.IsMatch(name, @"^[\w\-'._@]*$");
+            return Regex.IsMatch(name, @"^[\w\ \-'._@]*$");
         }
 
         private IAuthenticationProvider GetAuthenticationProvider(User user)