Refactor `User#suggest_name`.

* Rename `email` to `string` as variable can be an email, username
  or any valid string.

app/models/user.rb

@@ -286,15 +286,11 @@ class User < ActiveRecord::Base
     user
   end
 
-  def self.suggest_name(email)
-    return "" if email.blank?
-    if email[/\A[^@]+/].present?
-      # email provided
-      email[/\A[^@]+/].tr(".", " ").titleize
-    else
-      # username/name provided
-      email[/[^@]+\z/].tr(".", " ").titleize
-    end
+  def self.suggest_name(string)
+    return "" if string.blank?
+    local_part = string[/\A[^@]+/]
+    suggestion = local_part.present? ? local_part : string[/[^@]+\z/]
+    suggestion.tr(".", " ").titleize
   end
 
   def self.find_by_username_or_email(username_or_email)