Allow SwitchUser.switch_back to be considered even when not calling

`#remember_user`.

We need to be able to tell the gem that we want the user to be
remembered so that we can switch back to it. It was unclear how it
should've been done, so this is making sure that we don't have to make
two calls to the `SwitchUser API`, just to make sure the original user
will be remembered.

Related Issue: flyerhzm/issues/55

app/controllers/switch_user_controller.rb

@@ -1,5 +1,5 @@
 class SwitchUserController < ApplicationController
-  before_action :developer_modes_only
+  before_action :developer_modes_only, :switch_back
 
   def set_current_user
     handle_request(params)
@@ -8,16 +8,17 @@ def set_current_user
   end
 
   def remember_user
-    # NOOP unless the user has explicity enabled this feature
-    if SwitchUser.switch_back
-      provider.remember_current_user(params[:remember] == "true")
-    end
-
     redirect_to(SwitchUser.redirect_path.call(request, params))
   end
 
   private
 
+  def switch_back
+    if SwitchUser.switch_back
+      provider.remember_current_user(params[:remember] == "true")
+    end
+  end
+
   def developer_modes_only
     raise ActionController::RoutingError.new('Do not try to hack us.') unless available?
   end