message: Don't copy empty array from conduit into sidre::Buffer
  Also: Improves an overeager warning message in `Buffer::copyBytesIntoBuffer`
  Only warn when both `src==nullptr` and `nbytes >0`.
diff: @@ -194,8 +194,11 @@ Buffer* Buffer::copyBytesIntoBuffer(void* src, IndexType nbytes)
  {
  if(src == nullptr || nbytes < 0 || nbytes > getTotalBytes())
  {
  - SLIC_CHECK_MSG(src != nullptr,
  + if(src == nullptr)
  + {
  + SLIC_CHECK_MSG(nbytes == 0,
  "Cannot copy data into Buffer from null pointer.");
  + }
  SLIC_CHECK_MSG(nbytes >= 0, "Cannot copy < 0 bytes of data into Buffer.");
  SLIC_CHECK_MSG(nbytes <= getTotalBytes(),
  "Unable to copy " << nbytes << " bytes of data into Buffer with "
  @@ -299,8 +302,14 @@ void Buffer::importFrom(conduit::Node& buffer_holder)
  {
  allocate();
  conduit::Node& buffer_data_holder = buffer_holder["data"];
  - copyBytesIntoBuffer(buffer_data_holder.element_ptr(0),
  - buffer_data_holder.total_strided_bytes());
  +
  + const auto num_bytes = buffer_data_holder.total_strided_bytes();
  + if(num_bytes > 0)
  + {
  + copyBytesIntoBuffer(buffer_data_holder.element_ptr(0), num_bytes);
  + }
  +
  + this->print();
  }
  }
  