ui: webauthn: fix stopping store upgrades on destroy

ui: webauthn: fix stopping store upgrades on destroy

`deactivate` is only triggered if we switch to a different tab on
the same navigation level, but if we switch to a completely different
component (e.g., fom `Options -> Others` to `Datastore foo`) we can
only work with the destroy event, use the before one as else we
cannot access the view controllers method anymore.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>