[ticket/12852] Make get_url_parts handle get variable with no value

PHPBB3-12852
[ticket/12852] Remove whitespace

PHPBB3-12852
[ticket/12852] Add space after if

PHPBB3-12852
[ticket/12852] Add unit tests

PHPBB3-12852
Merge pull request #2919 from Senky/ticket/12852

[ticket/12852] Make get_url_parts handle get variable with no value

* Senky/ticket/12852:
  [ticket/12852] Add unit tests
  [ticket/12852] Add space after if
  [ticket/12852] Remove whitespace
  [ticket/12852] Make get_url_parts handle get variable with no value