Merge pull request #561 from Brendan-csel/Marlin_v1

Fix for Viki LCD issues printing from SD card

Marlin/ultralcd.cpp

@@ -96,6 +96,7 @@ static void menu_action_setting_edit_callback_long5(const char* pstr, unsigned l
     if (encoderPosition > 0x8000) encoderPosition = 0; \
     if (encoderPosition / ENCODER_STEPS_PER_MENU_ITEM < currentMenuViewOffset) currentMenuViewOffset = encoderPosition / ENCODER_STEPS_PER_MENU_ITEM;\
     uint8_t _lineNr = currentMenuViewOffset, _menuItemNr; \
+    bool wasClicked = LCD_CLICKED;\
     for(uint8_t _drawLineNr = 0; _drawLineNr < LCD_HEIGHT; _drawLineNr++, _lineNr++) { \
         _menuItemNr = 0;
 #define MENU_ITEM(type, label, args...) do { \
@@ -108,7 +109,7 @@ static void menu_action_setting_edit_callback_long5(const char* pstr, unsigned l
                 lcd_implementation_drawmenu_ ## type (_drawLineNr, _label_pstr , ## args ); \
             }\
         }\
-        if (LCD_CLICKED && (encoderPosition / ENCODER_STEPS_PER_MENU_ITEM) == _menuItemNr) {\
+        if (wasClicked && (encoderPosition / ENCODER_STEPS_PER_MENU_ITEM) == _menuItemNr) {\
             lcd_quick_feedback(); \
             menu_action_ ## type ( args ); \
             return;\
@@ -694,6 +695,8 @@ static void lcd_sd_updir()
 
 void lcd_sdcard_menu()
 {
+    if (lcdDrawUpdate == 0 && LCD_CLICKED == 0) 
+        return;	// nothing to do (so don't thrash the SD card)
     uint16_t fileCnt = card.getnrfilenames();
     START_MENU();
     MENU_ITEM(back, MSG_MAIN, lcd_main_menu);