Allow negative recover-swap length from LCD

Marlin/ultralcd.cpp

       MENU_ITEM_EDIT(float52, MSG_CONTROL_RETRACT_ZLIFT, &retract_zlift, 0, 999);
       MENU_ITEM_EDIT(float52, MSG_CONTROL_RETRACT_RECOVER, &retract_recover_length, -100, 100);
       #if EXTRUDERS > 1
-        MENU_ITEM_EDIT(float52, MSG_CONTROL_RETRACT_RECOVER_SWAP, &retract_recover_length_swap, 0, 100);
+        MENU_ITEM_EDIT(float52, MSG_CONTROL_RETRACT_RECOVER_SWAP, &retract_recover_length_swap, -100, 100);
       #endif
       MENU_ITEM_EDIT(float3, MSG_CONTROL_RETRACT_RECOVERF, &retract_recover_feedrate_mm_s, 1, 999);
       END_MENU();