Cargo IsFull and RenderLandingCraft use of IsFull.

I did this in two separate commits because the latter may not be desired but I thought it served as a nice indicator for the transport being unable to take more passengers.

I know we have HasSpace(int) already but I feel this is easier to read and makes a bit more sense than checking if (cargo.HasSpace(0)).

If this is not wanted please close to prevent clutter.