Prerequisites:
You'll need a machine with NVIDIA GPU having latest NVIDIA drivers (416.81). You can also reproduce the issue on AMD GPU having 18.10.2 or 18.11.1 drivers.

Steps to repro:
1. Open attached project and 'ProgressiveLightmappingExample' scene;
2. In the Lighting window select Progressive GPU (Preview) lightmapper;
3. In the Lighting window press 'Generate Lighting' button.

Actual result:

Baking stalls with the following error:

OpenCL Error: 'cl_int _err = kernelWrapper.CreateCLKernel(program, name, pvrJobType)' returned -44 (CL_INVALID_PROGRAM)!
[00:01:20] Enlighten: Finished 1 Create Input Lighting job (0.00s execute, 0.00s integrate, 0.85s wallclock)
LightmapEditorSettings: switching bake backend from 2 to 1.
gi::BakeBackendSwitch: Clear() active clients.
[EnlightenBakeManager] m_Clear = false;
OpenCL Error. Falling back to CPU lightmapper. Error callback from context: CL_INVALID_PROGRAM

without falling back to CPU Lightmapper

Expected result:
Editor doesn't crash and lightmapper falls back to CPU Lightmapper. Appropriate warning message is shown.

Notes:
- Reproducible in 2019.1.0a9, 2018.3.0b10;
- Reproducible with both NVIDIA (416.81 driver) and AMD GPU (18.10.2 and 18.11.1 drivers);
- Reproducible on GeForce 640M GPU with NVIDIA driver ver. 350.12 WHQL (OpenCL version 1.2).

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Fixed in 2019.2, 2019.1.0a14 and 2018.3.3f1