Continuous filename scrolling (#13609)

Marlin/src/lcd/ultralcd.cpp

@@ -809,10 +809,13 @@ void MarlinUI::update() {
     #if HAS_LCD_MENU && ENABLED(SCROLL_LONG_FILENAMES)
       // If scrolling of long file names is enabled and we are in the sd card menu,
       // cause a refresh to occur until all the text has scrolled into view.
-      if (currentScreen == menu_sdcard && filename_scroll_pos < filename_scroll_max && !lcd_status_update_delay--) {
-        lcd_status_update_delay = 6;
+      if (currentScreen == menu_sdcard && !lcd_status_update_delay--) {
+        lcd_status_update_delay = 4;
+        if (++filename_scroll_pos > filename_scroll_max) {
+          filename_scroll_pos = 0;
+          lcd_status_update_delay = 12;
+        }
         refresh(LCDVIEW_REDRAW_NOW);
-        filename_scroll_pos++;
         #if LCD_TIMEOUT_TO_STATUS
           return_to_status_ms = ms + LCD_TIMEOUT_TO_STATUS;
         #endif