Fix useless Z move before switching layer

CURA-12268
This was introduced while moving positions to 3D points. The Z offset of the travel move now has to be correct, otherwise we will move the nozzle up for next layer, then move back down for the travel move, then move up again when actually starting to print.

src/LayerPlan.cpp

@@ -2748,6 +2748,7 @@ void LayerPlan::writeGCode(GCodeExport& gcode)
                     gcode.writeTravel(current_position, extruder.settings_.get<Velocity>("speed_z_hop"));
 
                     // Prevent the final travel(s) from resetting to the 'previous' layer height.
+                    path.z_offset = final_travel_z_ - z_;
                     gcode.setZ(final_travel_z_);
                 }
                 for (size_t point_idx = 0; point_idx + 1 < path.points.size(); point_idx++)