Add a the default width to the output if no width is set
If css_styled_content is used for alternative output, there can't be no width calculcated because lastImageInfo won't be filled (e.g. by showing videos). Until now a width in the content element needs to be set - otherwise it will be 0 which is wrong and breaks the output - please see attached screenshots.
If it is 0 (why ever), don't just set it to 0 but to the default width (which is set in the constant editor)
(issue imported from #M11880)