Adding an external device after a Manager is created causes segmentation faults #1728

TEST(OCLExtContext, set)
{
    cl_device_id deviceId = NULL;
    cl_context context = NULL;
    cl_command_queue queue = NULL;

    af_print(af::randu(5,5)); // Remove this line and code works
    getExternals(deviceId, context, queue);
    afcl::addDevice(deviceId, context, queue);
    afcl::setDevice(deviceId, context);
    af::info();

    const int x = 5;
    const int y = 5;
    const int s = x * y;
    af::array a = af::constant(1, x, y);
    vector<float> host(s);
    a.host((void*)host.data());
    for (int i=0; i<s; ++i)
        ASSERT_EQ(host[i], 1.0f);
}