error: "ID3v2 TXXX data is not properly structured" when TXXX contains a string

[qippur]

In case TXXX field contains a string like:
TXXX (User defined text information): (Acoustid Id): 798f47ea-e816-4d90-a1a0-8032ea025268
write function throws an error:
"ID3v2 TXXX data is not properly structured"

Proposal: add string check - from line 633.

                case 'TXXX':
                    foreach ($valuearray as $key => $txxx_data_array) {
                        if (is_string($txxx_data_array)) {
                            $tag_data_id3v2['TXXX'][$key] = $txxx_data_array;
                        } elseif (isset($txxx_data_array['description']) && isset($txxx_data_array['data'])) {
                            $tag_data_id3v2['TXXX'][] = $txxx_data_array;
                            } else {
                                $this->errors[] = 'ID3v2 TXXX data is not properly structured';
                                return false;
                            }
                        }
                    }
                    break;