Mermaid and Headertabs

[RNitzsche]

Thanks for the mermaid-Extension.

We use Headertabs (https://www.mediawiki.org/wiki/Extension:Header_Tabs) and Accordions from the bootstrap extension. (https://www.mediawiki.org/wiki/Extension:Bootstrap)

Both extensions hide some parts of the page on opening. The user can switch to another heaedertab and will get further information.

Mermaid-Diagramms which are visibile when opening the page are rendered correctly.

Mermaid-Diagramms which are not visible when opening the page are not rendered when switching to the Headertab.

Maybe a small change in eventhandling could solve this problem. This would be great!