ExternalProject: Avoid repeating download verification

Verify step for downloaded files will be performed in separate script.

Modules/ExternalProject.cmake

@@ -1928,6 +1928,7 @@ function(_ep_add_download_command name)
           set(steps "download, verify and extract")
         endif ()
         set(comment "Performing download step (${steps}) for '${name}'")
+        file(WRITE "${stamp_dir}/verify-${name}.cmake" "") # already verified by 'download_script'
       else()
         set(file "${url}")
         if (no_extract)
@@ -1936,8 +1937,8 @@ function(_ep_add_download_command name)
           set(steps "verify and extract")
         endif ()
         set(comment "Performing download step (${steps}) for '${name}'")
+        _ep_write_verifyfile_script("${stamp_dir}/verify-${name}.cmake" "${file}" "${hash}")
       endif()
-      _ep_write_verifyfile_script("${stamp_dir}/verify-${name}.cmake" "${file}" "${hash}")
       list(APPEND cmd ${CMAKE_COMMAND} -P ${stamp_dir}/verify-${name}.cmake
         COMMAND)
       if (NOT no_extract)