Fixes #5699

It's either this or change random Next() to silently ignore incorrect arguments.
> This max(1, ...) thing is obfuscating the real logic.

Right you are, I didn't understand what it does.

Should I change it with a check like:
```csharp
var maxAdditionalDensity = resourceType.Info.MaxDensity - resLayer.GetResourceDensity(cell);
if (maxAdditionalDensity > 0)
    resLayer.AddResouce(resourceType, cell, world.SharedRandom.Next(1, maxAdditionalDensity));
```