cmake: update ocv_download

modules/dnn/cmake/OpenCVFindLibProtobuf.cmake

@@ -36,6 +36,7 @@ else()
                  "$ENV{OPENCV_PROTOBUF_URL}"
                  "https://github.com/google/protobuf/releases/download/v3.1.0/"
                DESTINATION_DIR "${PROTOBUF_CPP_PATH}"
+               ID PROTOBUF
                STATUS res
                UNPACK RELATIVE_URL)
   if(NOT res)

modules/xfeatures2d/cmake/download_boostdesc.cmake

@@ -26,6 +26,7 @@ function(download_boost_descriptors dst_dir status_var)
                    "$ENV{OPENCV_BOOSTDESC_URL}"
                    "https://raw.githubusercontent.com/opencv/opencv_3rdparty/${OPENCV_3RDPARTY_COMMIT}/"
                  DESTINATION_DIR ${dst_dir}
+                 ID "xfeatures2d/boostdesc"
                  RELATIVE_URL
                  STATUS res)
     if(NOT res)

modules/xfeatures2d/cmake/download_vgg.cmake

@@ -20,6 +20,7 @@ function(download_vgg_descriptors dst_dir status_var)
                    "$ENV{OPENCV_VGGDESC_URL}"
                    "https://raw.githubusercontent.com/opencv/opencv_3rdparty/${OPENCV_3RDPARTY_COMMIT}/"
                  DESTINATION_DIR "${dst_dir}"
+                 ID "xfeatures2d/vgg"
                  RELATIVE_URL
                  STATUS res)
     if(NOT res)