How to reproduce:
1. Open the attached "BundlesCrash" project and scene "1"
2. Go to BuildBundles--> Start (custom Menu items)
3. Enter playmode and select Terrain GameObject in Hierarchy
4. In the Inspector, below the "Test Load" script component, mark "Load" as true

Result - Crash occurs on:

========== OUTPUTING STACK TRACE ==================

0x0000000140F45085 (Unity) GetColorBlockColors
0x0000000140F4695C (Unity) DecompressDXT5Impl<void (__cdecl*)(DXTColBlock const * __ptr64,Color8888 * __ptr64 const)>
0x0000000140F4F121 (Unity) DecompressNativeTextureFormat
0x0000000140F5218C (Unity) Texture2D::GetPixels32
0x00000001415173F0 (Unity) SplatDatabase::RecalculateBasemap

Regression introduced in - 2017.1.0a3
Reproducible with - 2017.3.0b1, 2017.2.0f1, 2017.1.1p2, 2017.1.0a3
Not reproducible with - 2017.1.0a2

Notes:
1. Issue only reproduces when texture is Read/Write disabled
2. Reproduced on Windows7/Windows8 and macOS Sierra 10.12.6. Issue did not reproduce on Windows 10. Could reproduce the issue only on Editor and not a on a built player