As discovered and discussed by pead in the dev chat, the activity chooser has undefined section ids in contributed course formats.

This was initially fine until I looked for the section ID within the section header for an ID then falling back to the initial button that we generate. Details can be seen in MDL-68235

Proposal, Maintain the logic introduced by the aforementioned MDL but only use the sectionDiv if it contains the data attribute of sectionid.

Also shows that we need to inform developers of contrib course formats that if they override the section_header() with the course renderer that they should include the sectionid if they want drag and drop sections to work correctly with the activity chooser.

Will take a look at this before the release.