users: fix /users?name=<username> being case sensitive.

Things like https://danbooru.donmai.us/users?name=Evazion didn't work.

app/controllers/users_controller.rb

@@ -26,7 +26,8 @@ class UsersController < ApplicationController
 
   def index
     if params[:name].present?
-      @user = User.find_by_name!(params[:name])
+      @user = User.find_by_name(params[:name])
+      raise ActiveRecord::RecordNotFound if @user.blank?
       redirect_to user_path(@user, variant: params[:variant])
       return
     end

test/functional/users_controller_test.rb

@@ -3,7 +3,7 @@ require 'test_helper'
 class UsersControllerTest < ActionDispatch::IntegrationTest
   context "The users controller" do
     setup do
-      @user = create(:user)
+      @user = create(:user, name: "bob")
     end
 
     context "index action" do
@@ -24,11 +24,16 @@ class UsersControllerTest < ActionDispatch::IntegrationTest
         assert_equal(User.count, response.parsed_body.css("urlset url loc").size)
       end
 
-      should "list all users for /users?name=<name>" do
+      should "redirect to the user's profile for /users?name=<name>" do
         get users_path, params: { name: @user.name }
         assert_redirected_to(@user)
       end
 
+      should "be case-insensitive when redirecting to the user's profile" do
+        get users_path, params: { name: @user.name.capitalize }
+        assert_redirected_to(@user)
+      end
+
       should "raise error for /users?name=<nonexistent>" do
         get users_path, params: { name: "nobody" }
         assert_response 404