QTextImageFormat and caching

When creating a QTextImageFormat and calling setName(name) on it several times where name is the name of image file, then the memory will be increased each time insertImage() is called on the text cursor This happens because the image is stored in a cache. This happens regardless of whether undo-redo is enabled or not. When undo-redo is not enabled there is no need to store the images into the cache.