Steps to reproduce:
1. Open user attached project
2. Play the scene
- Unity crashes at this point

Expected result: unity should not crash when a texture atlas of zero pixel Texture2D is created

Reproduced in: 2018.3.a3, 2018.2.0b9, 2018.1.6f1, 2017.4.6f1, 2017.3.2f1, 2017.2.3p1

Fixed in: 2018.3.0a7

0x00000001403BA80D (Unity) PackTextureAtlas
0x00000001403BBCFF (Unity) PackTextureAtlasSimple
0x000000014135019D (Unity) Texture2D_CUSTOM_PackTextures
0x0000000035F816CC (Mono JIT Code) (wrapper managed-to-native) UnityEngine.Texture2D:PackTextures (UnityEngine.Texture2D[],int,int,bool)
0x0000000035F8151D (Mono JIT Code) [C:\buildslave\unity\build\artifacts\generated\common\runtime\TextureBindings.gen.cs:413] UnityEngine.Texture2D:PackTextures (UnityEngine.Texture2D[],int,int)
0x0000000035F8107E (Mono JIT Code) [D:\Downloads\case_1051229-MainSpace_v2 - Copy\Assets\Terrain\TerrainBuilder.cs:99] VTerrain.TerrainBuilder:MakeMainTexture ()
...