It looks like your current script will run the same even if you remove the go to portal row step. I suppose it might cause the row to highlight as active if it is not already so highlighted, but that's about it for that step. (You can't get the active portal row number until you are already on the active portal row so you are telling the script to go to the portal row where it is already at.)
Instead of looping through portal rows, it's a bit better to either pull up a found set of authors using Go To Related records or generate a list of ID's in a variable and then loop through those variables or records.
Much depends on your underlying data model which you do not share in your original post. One key question is whether all co-authors equally share in every such payment or if there are cases where one author gets a larger piece of the payment than a co-author.