Fix encoder position for sddirectory

Marlin/src/lcd/ultralcd.cpp

       encoderTopLine = 0;
       encoderPosition = 2 * ENCODER_STEPS_PER_MENU_ITEM;
       screen_changed = true;
+      first_page = false;
       lcdDrawUpdate = LCDVIEW_CLEAR_CALL_REDRAW;
     }