Fix null exception due to duration_t of zero (#12207)

Marlin/src/lcd/extensible_ui/ui_api.cpp

   }
 
   uint32_t getProgress_seconds_elapsed() {
-    const duration_t elapsed = IFPC(print_job_timer.duration(), 0);
-    return elapsed.value;
+    return IFPC(print_job_timer.duration(), 0);
   }
 
   #if ENABLED(PRINTCOUNTER)