message: core(ocl): handle NULL in dumpValue() debug call
  NULL is used for allocation of workgroup local variables
diff: @@ -2981,6 +2981,8 @@ bool Kernel::empty() const
  static cv::String dumpValue(size_t sz, const void* p)
  {
  + if (!p)
  + return "NULL";
  if (sz == 4)
  return cv::format("%d / %uu / 0x%08x / %g", *(int*)p, *(int*)p, *(int*)p, *(float*)p);
  if (sz == 8)
  