Players in spectator mode are unable to use inventory menus

Players in spectator mode are currently unable to use inventory menus. For example, you cannot use the /scenarios menu to edit scenarios as an admin, if you are in spectator mode.

The reason is that we are currently ignoring cancelled click events, but click events from spectator mode players are always set as cancelled by Spigot: https://hub.spigotmc.org/stash/projects/SPIGOT/repos/craftbukkit/commits/d4eaf226f97d66f35f4a62bf07626646ea2ec0b0

It should (hopefully) be safe to just treat all click events as valid clicks (even cancelled events), since the cancellation refers to the outcome of the event (the click itself has already happened).