Merge branch 'dz-handle-unmatched-routes' into 'master'

Handle unmatched routing with not_found method

## What does this MR do?

Handle all unmatched routes with 404 method

## Why was this MR needed?

We need this to prevent routing error when user access URL like /123 when there is no resource located under such name. 

## What are the relevant issue numbers?

Related to https://gitlab.com/gitlab-org/gitlab-ce/issues/23378 and https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6733.

See merge request !6905

app/controllers/application_controller.rb

@@ -45,6 +45,10 @@ class ApplicationController < ActionController::Base
     redirect_to request.referer.present? ? :back : default, options
   end
 
+  def not_found
+    render_404
+  end
+
   protected
 
   # This filter handles both private tokens and personal access tokens

config/routes.rb

@@ -88,4 +88,6 @@ Rails.application.routes.draw do
   get ':username.keys' => 'profiles/keys#get_keys', constraints: { username: /.*/ }
 
   root to: "root#index"
+
+  get '*unmatched_route', to: 'application#not_found'
 end

spec/requests/git_http_spec.rb

@@ -412,9 +412,10 @@ describe 'Git HTTP requests', lib: true do
 
         context "when the params are anything else" do
           let(:params) { { service: 'git-implode-pack' } }
+          before { get path, params }
 
-          it "fails to find a route" do
-            expect { get(path, params) }.to raise_error(ActionController::RoutingError)
+          it "redirects to the sign-in page" do
+            expect(response).to redirect_to(new_user_session_path)
           end
         end
       end