Back to site links to wrong path in case the last path visited is 404 page

Problem Motivation

Back to site links to wrong path in case the last path visited in *Page not found* page.

Steps to reproduce

1. Login as an admin
2. Visit a page that does exist - for example the front page.
3. Visit any page which does not exist: For example: http://example.com/not-found
   
4. Goto any page that exist, for example Modules page
   
5. Goto any other page that also exists, for example the config page
   
6. Click *Back to site*. It links to 404 page in step 2, instead of page in step 5
   

Proposed resolution

Remaining Tasks

See comment #66 -> #69.
Convert to MR

API Changes

None