characterData called twice

hi,
when parsing an ods document, if a character of more than 1 byte is found the parser calls "characterData" more than once. I should do this work around in lines 184 and 188

$this->sheets[$this->currentSheet]['rows'][$this->currentRow][$this->currentCell]['value'] .= $data;

instead of

$this->sheets[$this->currentSheet]['rows'][$this->currentRow][$this->currentCell]['value'] = $data;