I wouldn't take this lightly. Remember what happened to Seles? That crazy German guy didn't threaten her, he just did it and completely ruined her career. I think that all bigger tournaments should have metal detectors and screen spectators.
maybe not so much but I have to say that I was very angry at the French Tennis Federation when I saw what happened in RG 2009 final and how much time the security guys needed to enter the court.
If the guy had been crazy he had all the time needed to make the same as what was done to Seles.
This time I have to say that I'm reassured that it's in China (and also very importantly because there's a warning as some rightly said), and I think Roger will as well, because you can be sure that there will be many policemen in the stadium and all over the court, ready to intervene.
From what I read, it was also the case for the US Open 1981 final between Borg and McEnroe because of the threats to Björn Borg : there were many policemen around the court.