But I tested just a few times. If somebody re-starts work on
LibreOfficeLight, and encounter hangs, hopefully they notice this
commit and try to un-comment-out the line in question.

I hadn't noticed that temporaryHackToInvokeCallbackHandlers() thing
before, maybe calling it in the iOS app being developed (in the
"online" repo) is necessary, and would help avoiding the hangs I
occasionally see in it?

Change-Id: I0f4d8c800024c43acb512d40efdfad71c229bec2