message: cmake: don't include protobuf on disabled DNN module
diff: @@ -2,6 +2,10 @@ if(WINRT)
  ocv_module_disable(dnn)
  endif()
  +if(DEFINED BUILD_opencv_dnn AND NOT BUILD_opencv_dnn)
  + return()
  +endif()
  +
  include(${OpenCV_SOURCE_DIR}/cmake/OpenCVFindLibProtobuf.cmake)
  if(NOT Protobuf_FOUND)
  ocv_module_disable(opencv_dnn)
  