How to reproduce:
1. Open the attached user project and "CrashTest" scene

Expected result: Scene opens and console prints out info about a missing splat ("TerrainData is missing splat texture 0")
Actual result: Editor crashes on:

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

0x0000000141A8658F (Unity) SplatDatabase::RecalculateBasemap
0x0000000141AA616F (Unity) TerrainData::AwakeFromLoad
0x0000000140A93B38 (Unity) AwakeFromLoadQueue::InvokePersistentManagerAwake
0x0000000140A98049 (Unity) AwakeFromLoadQueue::PersistentManagerAwakeFromLoad
0x0000000140A981B9 (Unity) PersistentManager::IntegrateAllThreadedObjects
0x0000000140A9D2A0 (Unity) PersistentManager::LoadAndIntegrateAllPreallocatedObjects
0x0000000140A9F896 (Unity) PersistentManager::ReadObject
0x00000001403910DB (Unity) PPtr<Object>::operator Object * __ptr64
0x0000000140DBC85E (Unity) NativeFormatImporter::EndImport
0x0000000141C19517 (Unity) AssetDatabaseV1::ImportAsset
0x0000000141C20654 (Unity) AssetDatabaseV1::UpdateAsset
0x0000000141C40B23 (Unity) AssetInterface::ProcessAssetsImplementation
0x0000000141C4263A (Unity) AssetInterface::StopAssetEditing
0x0000000141C456AD (Unity) AssetInterface::Refresh
0x00000001411E7453 (Unity) Application::InitializeProject
0x000000014140EEEF (Unity) WinMain
0x0000000141E5AAB8 (Unity) __tmainCRTStartup
0x00007FFD14DF2774 (KERNEL32) BaseThreadInitThunk
0x00007FFD16F40D51 (ntdll) RtlUserThreadStart

========== END OF STACKTRACE ===========

Regression introduced in - 2018.1.0a2, 2017.3.0b6, 2017.2.0p1, 2017.1.2p2
Reproducible with - 2018.1.0a2, 2017.3.0b7, 2017.3.0b6, 2017.2.0p1, 2017.1.2p2
Not reproducible with - 2018.1.0a1, 2017.3.0b5, 2017.2.0f3, 2017.1.2p1

Note: Crash also happens when building the scene that contains a missing texture

=============== FIXED ====================
2017.1.2p3, 2017.2.0p2, 2017.3.0b9 and 2018.1.0a4.