Fix of custom multi copying first level into other higher ones

[GladieUO]

So i compared the old code with the new one, and there seems to be some mismatches with n16_narrow_n8 and n32_narrow_n8_checked making it dont work.
I also added one condition that was missing, and one extra line.

No idea if its proper fix, however it works.

#1478

[cbnolok]

Thanks for the research and good finding!
Could you check if the problem lies only in the last cast (in GetPlaneZ)? The other casts look legit and i prefer having a widespread use of the named casts to get an immediate idea both of the input and output types.
Also, naword wPlaneBuffer[PLANEDATA_BUFFER]{} declaration should already zero-initialize the array (because of the ending {}), so memset should be redundant.

[GladieUO]

I tried like 10 different variants, but nothing just this worked. Removing the memset breaks this too, just tried that, together with the GetPlaneZ -> if I change only this, it will break the movement between the floors in customizer.

[cbnolok]

Thank you, i'd ask you the last favor: could you log the values of both the named cast and the static cast? To see where and how they do differ

[GladieUO]

So I tried to log both the named and static, and both showed same numbers, which points to it being fine. So I reverted the whole fix, and added only the memset(wPlaneBuffer, 0, sizeof(wPlaneBuffer)); part. And its working just with that.

[cbnolok]

Okay it looks like zero-init via naword wPlaneBuffer[PLANEDATA_BUFFER]{} doesn't work because of silly C++ rules (might not be considered as a POD/aggregate type because of inheritance and custom constructors/disabled templated assignment operators). Memset is the way to go then, merging