Minor tweak to main menu

Marlin/src/lcd/menu/menu_main.cpp

   START_MENU();
   MENU_BACK(MSG_WATCH);
 
-  const bool busy = printer_busy();
+  const bool busy = printer_busy(),
+    #if ENABLED(SDSUPPORT)
+      card_detected = card.isDetected(),
+      card_open = card_detected && card.isFileOpen()
+    #endif
+  ;
 
   if (busy) {
     MENU_ITEM(function, MSG_PAUSE_PRINT, lcd_pause);
         if (!busy) MENU_ITEM(function, MSG_AUTOSTART, card.beginautostart);
       #endif
 
-      if (card.isDetected()) {
-        if (!card.isFileOpen()) {
+      if (card_detected) {
+        if (!card_open) {
           MENU_ITEM(submenu, MSG_CARD_MENU, menu_sdcard);
           #if !PIN_EXISTS(SD_DETECT)
             MENU_ITEM(gcode, MSG_CHANGE_SDCARD, PSTR("M21"));  // SD-card changed by user
       if (!busy) MENU_ITEM(function, MSG_AUTOSTART, card.beginautostart);
     #endif
 
-    if (card.isDetected()) {
-      if (!card.isFileOpen()) {
+    if (card_detected) {
+      if (!card_open) {
         MENU_ITEM(submenu, MSG_CARD_MENU, menu_sdcard);
         #if !PIN_EXISTS(SD_DETECT)
           MENU_ITEM(gcode, MSG_CHANGE_SDCARD, PSTR("M21"));  // SD-card changed by user