jquery.makeCollapsible: Enable passthru for links in premade toggle

Clicking on a regular link inside a premande toggle is supposed
to follow the link instead of collapsing/expanding the
appropriate element.

Broken during a rewrite in Id3f457a8 (2638b16c) - the comment
reflected the intended behavior, but the code was wrong.

(This is slightly different than the commit on master, as the
proper way to do this depends on several other commits being merged.
I'm backporting only the minimal fix.)

Bug: 46848
Change-Id: Id571f8d612e5131845d381121604c2b1116a077f