fixes a bug (reported by Pawel)

Section A
<?php
$_GET['bib']='listA.bib';
$_GET['all']=1;
include( 'bibtexbrowser.php' );
?>

Section B
<?php
$_GET['bib']='listB.bib';
$_GET['all']=1;
include( 'bibtexbrowser.php' );
?>

Bug: both times it displays the entries from only listA.bib.

Fix: if (!isset($_GET[Q_DB]) || !$_GET[Q_DB]->is_already_loaded($_GET[Q_FILE])) { setDB(); }