Initial Value in FIB

It seems the default initial value of FIB being 0 can cause underapproximations of value in some cases (maybe just with large state spaces and insufficient iterations?). To ensure FIB always returns an upper bound, should this be initialized to `Inf` or something else by default?

The logic for checking if the initial value is finite already seems to be present here:
https://github.com/JuliaPOMDP/NativeSARSOP.jl/blob/f9beca15c222fa79d8ff734422429776923db474/src/fib.jl#L71-L77