[ticket/11437] avoid $start becoming negative when no search results are found

When search returns no results there is no need to go inside the if
statement. Since $result_count becomes zero, $start becomes negative
which leads to failed assertion.

PHPBB3-11437
[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
Merge branch 'develop-olympus' into develop

* develop-olympus:
  [ticket/11617] Remove spaces and tabs from empty lines
  [ticket/11617] Missing U_ACTION in acp_captcha.php
Merge remote-tracking branch 'dhruvgoel92/ticket/11437' into develop

* dhruvgoel92/ticket/11437:
  [ticket/11437] avoid $start becoming negative when no search results are found