Update mysqli.php

### Tracker

http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=33916&start=0

### How to test

1. Install a clean joomla
2. add a extra table with a # as the first letter  (e.g. #_helpdesk_categories)
3. Access the System Information (BE --> System --> System Information)
4. You get a SQL error like
*You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '' at line 1 SQL=SHOW FULL COLUMNS FROM #_helpdesk_categories*
5. apply patch
6. test again

### joomla-bugs.de Referenze
http://www.joomla-bugs.de/forum/index.php?topic=608