ES2 Fallback Fails on Nougat Devices that do not support Vulkan

Discovered this while doing RC candidate testing for 4.13

Works fine in all other use cases:
Nougat devices that support Vulkan
Marshmallow devices that support Vulkan
Marshmallow devices that don't support Vulkan.

1. Package a project for es2 and Vulkan.
2. Install on a device running Android 7.0 that does not support Vulkan (Nexus 9 4068)
3. Launch the app.
4. Observe the crash.

08-28 13:16:25.156: D/UE4(13728): Assertion failed: GpuCount >= 1 [Link Removed] [Line: 542]
08-28 13:16:25.156: D/UE4(13728): libUE4.so!FDebug::LogAssertFailedMessage(char const*, char const*, int, wchar_t const*, ...)
08-28 13:16:25.156: D/UE4(13728): libUE4.so!FVulkanDynamicRHI::InitInstance()
08-28 13:16:25.156: D/UE4(13728): libUE4.so!FVulkanDynamicRHI::Init()
08-28 13:16:25.156: D/UE4(13728): libUE4.so!RHIInit(bool)
08-28 13:16:25.156: D/UE4(13728): libUE4.so!FEngineLoop::PreInit(wchar_t const*)
08-28 13:16:25.156: D/UE4(13728): libUE4.so!FEngineLoop::PreInit(int, wchar_t*, wchar_t const)
08-28 13:16:25.156: D/UE4(13728): libUE4.so!AndroidMain(android_app*)
08-28 13:16:25.156: D/UE4(13728): libUE4.so!android_main()
08-28 13:16:25.156: D/UE4(13728): libUE4.so![Unknown]()
08-28 13:16:25.156: D/UE4(13728): libc.so![Unknown]()
08-28 13:16:25.156: D/UE4(13728): libc.so![Unknown]()
08-28 13:16:25.157: D/UE4(13728): [2016.08.28-17.16.25:157][ 0]Assertion failed: Assertion failed: GpuCount >= 1 [Link Removed] [Line: 542]