Fix duplicates in item view

[joveeater]

Summary

SUMMARY: Bugfixes "Prevent duplicates in the item view when 3d vision is on"

Purpose of change

No more duplicates.

Describe the solution

Better math on the iteration over z levels, it was doing 0 twice.

[olanti-p]

There seems to be an off-by-one error somewhere.

Repro steps:

1. Set Vertical range of 3D field of vision to 1
2. Spawn as the default evacuee in a refugee shelter
3. Drop a knife near the entrance
4. Climb on the rooftop
5. You can see the knife when in "Look around" mode (x)
6. Open V, see the knife is not there

[joveeater]

Yep, right you are. It was missing the lowest z level.