Make sure event handlers are set up even if onready handler is lost

Due to a jQuery bug, errors in local code (gadgets, user scripts)
can cause onready handlers to not be executed. For MMV this causes
catastrophic failure, with a black screen of death on exit.

This change makes sure that the setup code necessary for Media
Viewer to work is executed at latest when MV is invoked, even if some
onready handlers were skipped.

Opening MediaViewer via a hash-URL will still not work if the onready
handler fails, but that's hard to avoid and it is not a catastrophic
failure anymore. This change can be reverted when bug 70772 gets fixed.

Bug: 70756
Change-Id: Ida3b780791bc9dfec29303567d33e3aa4f44dd81
Mingle: https://wikimedia.mingle.thoughtworks.com/projects/multimedia/cards/891
(cherry picked from commit 4b6e44a2fcecc5bb316748a364727d20bcea7eff)