FIX BUG: Terrain mesh is randomly broken because of brick's top face

[stone-SJH]

PR: #2

In the WorldGenerationTest.unity scene, you're generating some huge mesh without setting Mesh.indexFormat to UInt32(the default value is UInt16), which causing meshes with vertex count > 65535 fail to render normally.
Unity doc here: https://docs.unity3d.com/ScriptReference/Mesh-indexFormat.html

However, using UInt32 indices format instead of UInt16 will probably drop performance and need more memory (for example, X-5 Z-3 ChunkSlice#4, which has 101920 verts and 221400 triangles, cost around 6.5MB for indices using UInt32 or around 1.5MB using UInt16). So a better solution might be split your huge meshes into sub-meshes(verts < 65535) and still using UInt16, if you have time, you can have a try about this :)

[tetreum]

Funny because you can see here

brickcraft/Assets/Scripts/World/WorldBehaviour.cs

Line 179 in 60e23c0

combinedMesh.indexFormat = UnityEngine.Rendering.IndexFormat.UInt32;

that is something that i already did when i was bruteforcing the entire brick model rather than the shown faces xDD And then i never thought of it again xDDD
The thing is, i belive it throwed me an error back then. Why isn't it doing the same in those cases?

[tetreum]

I've added you to https://github.com/tetreum/brickcraft#credits and also on https://tetreum.github.io/brickcraft/?/help
Thank you so much!