#009031: PersistentObject in-memory cache code causes warnings

In lib/ezdb/classes/ezmysqldb.php:

if ( stristr( $sql, "update" ) )
{
    $queryParts = preg_match( "/(update[\s]*)(low_priority[\s*])?(ignore[\s*])?([\s\w,]*)([\s]set[\s].*)/",
                                                  strtolower( $sql ),
                                                  $matches );
    foreach( explode( ",", $matches[4] ) as $tableName )
    {
                            eZPersistentObject::clearObjectCache( $tableName );
    }

stristr and the regular expression will will also match any field values of a SQL INSERT query (e.g. the default subtree notification mails that mention the word "update"), and then there will be a warning:

Warning: (PHP)
Undefined offset:  4 in /srv/ezpublish/sites/projects/lib/ezdb/classes/ezmysqldb.php on line 485

The same counts for the detection of insert and delete queries.

Version: trunk (pre 3.9alpha1)
PHP Version:
Webserver:
Database: