Fix issue when no organ is created for a scale

[lailanhabibah]

In XPalm for example we may ask for the female output, but no female is created during the simulation. We have the Female scale in the output, but the vector of statuses is empty. The thing is that we index the first status in this vector at this point:

https://github.com/VirtualPlantLab/PlantSimEngine.jl/blob/a3abf9ef4222dc9ac094260c17fced0abd4643e2/src/mtg/GraphSimulation.jl#L115C5-L115C60

And it returns a bounds error. We should first check if we have outputs at this scale, and if not continue with the next scale.

[VEZY]

Proposition:

filter!(kv -> !isempty(kv[2]), outs)

Put this on the beginning of the function (decide if mutating or copying first). Also, with this modification we can remove the test on the length on the for loop.