This assumes we know the pornstar is dead and unless you already found that out, how can you know?
Pornstars are not famous outside their world, so they don't get to be on mainstream news and TV shows, etc.
Granted, some people who featured in the Golden Age of Porn are likely to be dead, but you would have to know that already, before watching a film they appeared in.
People die all the time and pornstars are no different.
I usually do not know that someone is dead before watching a film. I only find this out if I want to see more of what they have done on iafd and then see that they have died.
I don't think I have ever felt bad about watching a film with someone in it who had died. Plus, we don't have any problem with watching old films with some or all who were in it now being dead, do we?