tOutputSize' bytes will be decoded.
  The function stops decoding on reaching this objective,
  which can boost performance when only the beginning of a block is required.

 @return : the number of bytes decoded in `dst` (necessarily <= dstCapacity)
           If source stream is detected malformed, function returns a negative result.

  Note : @return can be < targetOutputSize, if compressed block contains less data.

  Note 2 : this function features 2 parameters, targetOutputSize and dstCapacity,
       