#125 digislice produces a single large file

[Willem van Straten]

... when it should produce multiple smaller slices. In this state, it repeated reports error messages like the following

dsp::Truncate::transformation end of data
dsp::Operation::operate exception
Error::stack
        dsp::Transformation[Truncate]::operation
        dsp::Truncate::transformation
        dsp::Truncate::transformation
Error::EndOfFile
Error::message
        input start_time=53873.3225579733767 >= end_epoch=53873.3225181891358

where the start_time changes but the end_time does not.

[Willem van Straten]

This appears to be owing to changes that I made to Operation::operate in April 2025:

8666c9194 (Willem van Straten 2025-04-29 11:42:39 +1200 107)

  try
  {
    //! call the pure virtual method defined by sub-classes
    operation();
  }
  catch (Error& error)
  {
    cerr << "dsp::Operation::operate exception " << error << endl;
    operation_status = -1;
  }

This change causes any exceptions to be swallowed; however, Truncate::operation throws a special exception that indicates EndOfFile ... swallowing this exception stops it from working as needed.