Include negative Z probe offset in clearance move

Marlin/Marlin_main.cpp

       // If the nozzle is above the travel height then
       // move down quickly before doing the slow probe
       float z = LOGICAL_Z_POSITION(Z_CLEARANCE_BETWEEN_PROBES);
+      if (zprobe_zoffset < 0) z -= zprobe_zoffset;
       if (z < current_position[Z_AXIS])
         do_blocking_move_to_z(z, MMM_TO_MMS(Z_PROBE_SPEED_FAST));