Returns the specified code-block in the current tile for the specified component (as a reference or copy).

       <p>The returned code-block may be progressive, which is indicated by
       the 'progressive' variable of the returned 'DataBlk' object. If a
       code-block is progressive it means that in a later request to this
       method for the same code-block it is possible to retrieve data which is
       a better approximation, since meanwhile more data to decode for the
       code-block could have been received. If the code-block is not
       progressive then later calls to this method for the same code-block
       will return the exact same data values.</p><p>The data returned by this method can be the data in the internal
       buffer of this object, if any, and thus can not be modified by the
       caller. The 'offset' and 'scanw' of the returned data can be
       arbitrary. See the 'DataBlk' class.</p>