dspsr fails in some cases

[abhisrkckl]

In the case of some raw data files, dspsr fails to fold the data. This results in no FITS file and an empty summary file. Such cases seem to work when dspsr is manually run with "-S 1" option.

It is not immediately clear from the logs what has happened.

[abhisrkckl]

I have added a check to see if the FITS file has been created in commit 93474de

This will warn the user if dspsr fails.

[abhisrkckl]

The root cause of this issue and why "-S 1" fixes it is not understood.

[abhisrkckl]

We should also have an option to run dspsr with -S 1 option.

[abhisrkckl]

Tested the temporary solution and it works. Need to investigate further.