Simulate logic adds extra case in which UCB is not used

I am not sure of the logic behind adding `ltn<= 0.0` in the simulate() function. It implies that for two first two tree queries (`ltn` = `-Inf` and `0`), it uses the node value as criterion. I understand that we use node value when `ltn = -Inf`, but don't understand why it is the case for `ltn = 0`

Ref [this line](https://github.com/JuliaPOMDP/BasicPOMCP.jl/blob/master/src/solver.jl#L72) in simulate()
```
for node in t.children[h]
n = t.n[node]
if n == 0 && ltn <= 0.0
criterion_value = t.v[node]
elseif
.
.
.
end
```