Steps to reproduce:

1) Download attached project and open in Unity
2) Make sure Graphics API is set to Vulkan in the Player Settings
3) Connect low-end device to your machine (which doesn't support Vulkan graphics API)
4) Build and run project on a device

Expected result: Warning should appear that there is no compatible device connected (check attached image 'expected.png')
Actual result: Application is pushed to device without any warning

Note: Warning appears when building using GLES3 (when device support only GLES2)

Reproduced with:
5.6.5p1, 2017.1.3f1, 2017.2.1p1, 2017.3.0p3, 2018.1.0b4

Devices under test(Note: both of them support only GLES2):
0065 Samsung Galaxy S5 Mini, OS: 5.1.1, CPU: Exynos 3 Quad, GPU: Mali-400MP4
0048 Samsung Galaxy S3, OS: 4.3, CPU: Samsung Exynos, GPU: Mali-400 MP