Make DRLA Supply Crates unopenable on the shelf

It was possible to shoot open a Supply Crate in the Outpost when it was
on sale as a Shop Special, which could possibly fling a weapon to you
over the counter, so this makes it invulnerable which prevents it from
ever being opened.
Shop Special blacklist: Time Sphere, Wings

No reason to ever buy these items in the Outpost since they are
immediate and do not carry over between levels.