Returns the specified coded code-block, for the specified component, in the current tile. The first layer to return is indicated by 'fl'. The number of layers that is returned depends on 'nl' and the amount of data available.

       <p>The argument 'fl' is to be used by subsequent calls to this method
       for the same code-block. In this way supplamental data can be retrieved
       at a later time. The fact that data from more than one layer can be
       returned means that several packets from the same code-block, of the
       same component, and the same tile, have been concatenated.</p><p>The returned compressed code-block can have its progressive
       attribute set. If this attribute is set it means that more data can be
       obtained by subsequent calls to this method (subject to transmission
       delays, etc). If the progressive attribute is not set it means that the
       returned data is all the data that can be obtained for the specified
       subblock.</p><p>The compressed code-block is uniquely specified by the current tile,
       the component (identified by 'c'), the subband (indentified by 'sb')
       and the code-bock vertical and horizontal indexes 'm' and 'n'.</p><p>The 'ulx' and 'uly' members of the returned 'DecLyrdCBlk' object
       contain the coordinates of the top-left corner of the block, with
       respect to the tile, not the subband.</p>