Only access cross_fill_patterns if it is filled
Only access cross_fill_patterns if it is filled

If it is not filled, pass a null pointer.
The vector is only filled for Cross, Cross 3D or future patterns that create a space filling tree.

Contributes to issue CURA-4095.

ROBO3D/CuraEngine,alephobjects/CuraEngine,alephobjects/CuraEngine,ROBO3D/CuraEngine,Ultimaker/CuraEngine,alephobjects/CuraEngine,ROBO3D/CuraEngine,Ultimaker/CuraEngine