Unset variables if not matched yet

Co-authored-by: Philippe Canal <pcanal@fnal.gov>

Author: Blake-Madden

cmake/modules/FindR.cmake

@@ -76,6 +76,8 @@ if(WIN32 AND R_EXECUTABLE MATCHES "R_EXECUTABLE-NOTFOUND")
         if (R_EXECUTABLE AND R_SCRIPT)
           break()
         endif()
+        unset(R_EXECUTABLE)
+        unset(R_SCRIPT)
       endif()
     endforeach()
   endif()