Fix error when sorted_channel_file is missing

[Kamleshbarik05]

This PR fixes an issue where the program continues running even if the sorted_channel_file does not exist.

Before:

• If the file path was wrong or missing, the error was ignored
• The program continued silently, which could lead to incorrect results

After:

• The code now checks whether the file exists
• If the file is missing, it raises a clear FileNotFoundError
• This helps users quickly understand what went wrong

This change prevents silent failures and makes debugging easier.

[Kamleshbarik05]

Hi @apd10,

I’ve added a proper validation for the missing "sorted_channel_file" and raising a clear error.

Could you please review it when you get time? Let me know if any changes are needed.

Thanks!