fixed build without ffmpeg (gpu module)

modules/gpu/CMakeLists.txt

@@ -53,16 +53,20 @@ if (HAVE_CUDA)
   unset(CUDA_nvcuvid_LIBRARY CACHE)
   find_cuda_helper_libs(nvcuvid)
 
-  if (WIN32)
+  if(WIN32)
     unset(CUDA_nvcuvenc_LIBRARY CACHE)
     find_cuda_helper_libs(nvcuvenc)
   endif()
 
-  set(cuda_link_libs ${CUDA_LIBRARIES} ${CUDA_npp_LIBRARY} ${CUDA_nvcuvid_LIBRARY} ${HIGHGUI_LIBRARIES})
+  set(cuda_link_libs ${CUDA_LIBRARIES} ${CUDA_npp_LIBRARY} ${CUDA_nvcuvid_LIBRARY})
 
-  if (WIN32)
+  if(WIN32)
     set(cuda_link_libs ${cuda_link_libs} ${CUDA_nvcuvenc_LIBRARY})
   endif()
+
+  if(WITH_FFMPEG)
+    set(cuda_link_libs ${cuda_link_libs} ${HIGHGUI_LIBRARIES})
+  endif()
 else()
   set(lib_cuda "")
   set(cuda_objs "")