Fixed bug where filtering led to 'Prelude.head: empty list'
While checking if header should be added or not I was not checking if the returned list is empty or not.
So, when doing ps |fsh -p table 'filter (\(pid:_)-> read pid > 90000)' which will return nothing if no PIDs are greater than 90000, the program will simply crash.
Now it displays proper header.