Fix printing time being shown without `M73` gcode

Adjust estimated times only if speed is changed. Printing time has to stay printing time.

Firmware/ultralcd.cpp

@@ -718,8 +718,12 @@ void lcdui_print_time(void)
             print_t = print_tr;
             suff = 'R';
         }
+        else
+        {
+            print_t = _millis() / 60000 - starttime / 60000; 
+        }
 
-        if (feedmultiply != 100)
+        if (feedmultiply != 100 && (print_tc != 0 || print_tr !=0))
         {
             suff_doubt = '?';
             print_t = 100ul * print_t / feedmultiply;