message: fix missing addref() in ocl::Context::create(str)
  fix
  unable to add related test cases as there is
  no public access to Context:Impl refcounts
diff: @@ -2437,6 +2437,7 @@ public:
  if (impl)
  {
  CV_LOG_INFO(NULL, "OpenCL: reuse context@" << impl->contextId << " for configuration: " << configuration)
  + impl->addref();
  return impl;
  }
  