Fix game crash when building a mega distillation tower in creative using hologram

[6C-C6]

Summary

Got a game crash when trying to build a mega distillation tower (new structure one), with

java.lang.IndexOutOfBoundsException: Index: 2, Size: 2

on function

gregtech.common.tileentities.machines.multi.MTEMegaDistillationTower.getCurrentLayerBottomOutputHatchCount(MTEMegaDistillationTower.java:373)

according to the crash report.

Fix it by adding the layer index by 1, and use index-1 for outputHatchesPerLayer.get().
Refrencing to the old structure's code:

GT5-Unofficial/src/main/java/bartworks/common/tileentities/multis/mega/MTEMegaDistillTowerLegacy.java

Line 207 in 6ad722c

return this.mOutputHatchesByLayer.size() < this.mHeight || this.mHeight <= 0 ? 0

where mHeight ranges in [1, tTotalHeight - 1], which is equal to the index of fluid output layers.

Also change the variable name from currentLayer to currentOutputLayer, as the previous one has already been used otherwhere in the code, refering to the layer index of middle pieces.

Checklist

• I have tested this PR in DevEnv
• I have tested this PR in Fullpack
• This PR is in compliance with the GTNH AI Policy
• This PR requires another PR in order to merge