Thumbnails of macros not always exported in HTML export

Some macros which are rendered as an image are not properly displayed in a HTML export of the space. They display a broken image or information about the macro.

Some others work as expected and the thumbnail image is added to the HTML export.

For example:

• The chart macro works as expected and the image is displayed in the HTML export.
• The view file renders as a broken image. Tested with a PDF file.