getDevices causes crash

[hujiajie]

In function WebCLDeviceList::WebCLDeviceList(WebCL* compute_context, cl_platform_id platform_id, int device_type), NULL is passed to webcl_clGetDeviceIDs as the device id pointer. The NULL pointer causes crash in GpuChannelHost::CallclGetDeviceIDs(...). The exact statement which results in the crash is devices[index] = (cl_device_id) point_device_list[index];.