Reads the current data value and writes it to writer.
If the EmberReader instance is currently placed on the start of a container, then skips to the end of the container, such that calling Read afterwards will place the reader on either a sibling of the container, the end of the parent container or the end of the stream.
This method has no effect, if the reader is currently placed on a data value with primitive encoding (the next call to Read will skip possibly unread contents anyway).
///
/// has never been called, or
/// The last call returned false or threw an exception.
/// has been called.
