Group the fail case in one negation (PR#2572)

Marlin/cardreader.cpp

@@ -481,8 +481,7 @@ void CardReader::write_command(char *buf) {
 }
 
 void CardReader::checkautostart(bool force) {
-  if (!force && (!autostart_stilltocheck || next_autostart_ms < millis()))
+  if (!(force || !autostart_stilltocheck || next_autostart_ms >= millis())) return;
-    return;
 
   autostart_stilltocheck = false;