FlattenGraphFilter assertion error

[Nicolás Lichtmaier]

Hi!

I was getting an exception in FlattenGraphFilter and, as I saw there was 
assertion statements nearby, I reran everything with assertions enabled. 
And I see it crashes here (FlattenGraphFilter.java:174)


At this point inputNode has all fields with -1 (except nextOut, which is 
0).. and outputFrom's value is 395.

The code is pretty complex, so before trying to undestand it I thought 
maybe someone could know what's happening just seeing this, maybe not. =)

I'll keep the debugging session open for a while in case some more 
variables could be useful to debug this.

Thanks!