Fixed include order issue. The cuda utils headers weren't including dlib/config.h before

the asserts that DLIB_USE_CUDA must be defined.  This only matters for users who try to
install dlib and use some build system that doesn't define DLIB_USE_CUDA, and so therefore need
dlib/config.h to define it for them.

dlib/cuda/cuda_data_ptr.h

@@ -3,11 +3,12 @@
 #ifndef DLIB_DNN_CuDA_DATA_PTR_H_
 #define DLIB_DNN_CuDA_DATA_PTR_H_
 
+#include "../assert.h"
+
 #ifdef DLIB_USE_CUDA
 
 #include <memory>
 #include <vector>
-#include "../assert.h"
 
 namespace dlib
 {

dlib/cuda/cuda_utils.h

@@ -3,12 +3,13 @@
 #ifndef DLIB_CUDA_UtILS_H_
 #define DLIB_CUDA_UtILS_H_
 
+#include "../algs.h"
+
 #ifndef DLIB_USE_CUDA
 #error "This file shouldn't be #included unless DLIB_USE_CUDA is #defined"
 #endif
 
 #include "cuda_errors.h"
-#include "../algs.h"
 #include <cmath>
 
 #include <cuda_runtime.h>