public boolean hasRecordsInBuffer() {
      return readRowsIndexInBuffer < recordsNumInValBuffer;
    }
Returns how many rows we fetched with next(). It only means how many rows
are read by next(). The returned result may be smaller than actual number
of rows passed by, because {@link #seek(long)},
{@link #nextColumnsBatch()} can change the underlying key buffer and
value buffer.

@return next row number
@throws IOException
ql/src/java/org/apache/hadoop/hive/ql/io/RCFile.java