Reads new data into the {@code RowSet}. The calling {@code RowSet} object
must itself implement the {@code RowSetInternal} interface and the
{@code RowSetReader} must be registered as a reader on the
{@code RowSet}.
This method adds rows into the calling {@code RowSet}. The reader may
invoke any of the {@code RowSet}'s methods except for the {@code execute}
method (calling {@code execute} will cause an {@code SQLException} to be
thrown). However, when the reader calls the {@code RowSet}'s methods, no
events are sent to listeners - any listeners are informed by the calling
{@code RowSet}'s {@code execute} method once the reader returns from the
{@code readData} method.
