[ticket/11617] Missing U_ACTION in acp_captcha.php

http://tracker.phpbb.com/browse/PHPBB3-11617

PHPBB3-11617
[ticket/11617] Remove spaces and tabs from empty lines

PHPBB3-11617
Merge remote-tracking branch 'VSEphpbb/ticket/11617' into develop-olympus

* VSEphpbb/ticket/11617:
  [ticket/11617] Remove spaces and tabs from empty lines
  [ticket/11617] Missing U_ACTION in acp_captcha.php