users: fix find_by_name for names with special characters.

`User.find_by_name` used `where_ilike` to do a case-insensitve name
search, but it didn't escape `*` or `\` characters first, so it didn't
handle names containing these characters properly.

app/models/application_record.rb

@@ -25,6 +25,10 @@ class ApplicationRecord < ActiveRecord::Base
         where.not("#{qualified_column_for(attr)} ILIKE ? ESCAPE E'\\\\'", value.mb_chars.to_escaped_for_sql_like)
       end
 
+      def where_iequals(attr, value)
+        where_ilike(attr, value.gsub(/\\/, '\\\\').gsub(/\*/, '\*'))
+      end
+
       # https://www.postgresql.org/docs/current/static/functions-matching.html#FUNCTIONS-POSIX-REGEXP
       # "(?e)" means force use of ERE syntax; see sections 9.7.3.1 and 9.7.3.4.
       def where_regex(attr, value)

app/models/user.rb

@@ -142,7 +142,7 @@ class User < ApplicationRecord
 
       # XXX downcasing is the wrong way to do case-insensitive comparison for unicode (should use casefolding).
       def find_by_name(name)
-        where_ilike(:name, normalize_name(name)).first
+        where_iequals(:name, normalize_name(name)).first
       end
 
       def normalize_name(name)