Fix delete language and script notes field (#2392)

[melaniekung]

No description provided.

[sevein]

I was testing this block from a new test file (test/phpunit/sfIsadPlugin/sfIsadPluginTest.php - feel free to use it!) and the last case listed in the table fails with this change, i.e. when the submitted value is empty and no note exists, $note contains the empty ArrayObject, so the call to the delete method produces:

Call to undefined method ArrayObject::delete()

Here's an alternative that passes in all four test cases. $note is consistently either a QubitNote or null, which I find a little easier to read:

case 'languageNotes':
    $notes = $this->resource->getMemoryNotesByType(['noteTypeId' => QubitTerm::LANGUAGE_NOTE_ID]);
    $note = $notes[0] ?? null;

    // Clear the stored note when the field is empty; otherwise create the
    // note if necessary and update its content.
    if (0 === strlen($value)) {
        if (null !== $note) {
            $note->delete();
        }

        break;
    }

    if (null === $note) {
        $note = new QubitNote();
        $note->typeId = QubitTerm::LANGUAGE_NOTE_ID;
        $note->userId = sfContext::getInstance()
            ->user
            ->getAttribute('user_id');

        $this->resource->notes[] = $note;
    }

    $note->content = $value;

    return $this;

[melaniekung]

thank you @sevein!