redirect to login page when linking to /files as unauth

test plan:
* in a new browser/incognito window, try to visit /files
* it should redirect to the login page

closes #CNVS-36611

Change-Id: Ie0d8e7b145e062b8aa9824c6c49c7ae2386f2d64
Reviewed-on: https://gerrit.instructure.com/110352
Tested-by: Jenkins
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
QA-Review: Deepeeca Soundarrajan <dsoundarrajan@instructure.com>
Product-Review: James Williams  <jamesw@instructure.com>

app/controllers/application_controller.rb

@@ -587,7 +587,7 @@ class ApplicationController < ActionController::Base
   def require_context
     get_context
     if !@context
-      if request.path.match(/\A\/profile/)
+      if @context_is_current_user
         store_location
         redirect_to login_url
       elsif params[:context_id]
@@ -664,6 +664,7 @@ class ApplicationController < ActionController::Base
         @context = api_find(CourseSection, params[:course_section_id])
       elsif request.path.match(/\A\/profile/) || request.path == '/' || request.path.match(/\A\/dashboard\/files/) || request.path.match(/\A\/calendar/) || request.path.match(/\A\/assignments/) || request.path.match(/\A\/files/) || request.path == '/api/v1/calendar_events/visible_contexts'
         # ^ this should be split out into things on the individual controllers
+        @context_is_current_user = true
         @context = @current_user
         @context_membership = @context
       end

spec/controllers/assignments_controller_spec.rb

@@ -39,7 +39,7 @@ describe AssignmentsController do
   describe "GET 'index'" do
     it "should throw 404 error without a valid context id" do
       #controller.use_rails_error_handling!
-      get 'index'
+      get 'index', :course_id => 'notvalid'
       assert_status(404)
     end