C API crashes when invalid mesh is used by a BVH or can't be cleaned up

[cadop]

Currently just experienced with Unity when creating a BVH with 0 vertices, the C API will crash when trying to use this invalid mesh for raycasting.

While this isn't a priority since it only happens when incorrectly setting the BVH, it would be nice to have a more graceful exit.

=================================================================
	Managed Stacktrace:
=================================================================
	  at <unknown> <0xffffffff>
	  at DHARTAPI.RayTracing.NativeMethods:DestroyRayTracer <0x00126>
	  at DHARTAPI.RayTracing.NativeMethods:C_DestroyRayTracer <0x00072>
	  at DHARTAPI.RayTracing.EmbreeBVH:ReleaseHandle <0x00072>
	  at System.Runtime.InteropServices.SafeHandle:DangerousReleaseInternal <0x00670>
	  at System.Runtime.InteropServices.SafeHandle:InternalFinalize <0x0009a>
	  at System.Runtime.InteropServices.SafeHandle:Dispose <0x000e2>
	  at System.Runtime.InteropServices.SafeHandle:Finalize <0x0006b>
	  at DHARTAPI.NativeUtils.NativeObject:Finalize <0x00142>
	  at System.Object:runtime_invoke_virtual_void__this__ <0x0018b>
=================================================================

and

0x00007FF88F7446DF (embree3) rtcReleaseScene
0x00007FF8A36CE273 (DHARTAPI) GetPathInfo
0x00007FF8A36C5573 (DHARTAPI) DestroyRayTracer

[cadop]

Crash also happens if a BVH or Graph is setup and isn't cleaned up.