Fix and improve G-code queue (#21122)

Co-authored-by: Scott Lahteine <thinkyhead@users.noreply.github.com>

Marlin/src/MarlinCore.cpp

@@ -407,7 +407,7 @@ void startOrResumeJob() {
  */
 inline void manage_inactivity(const bool ignore_stepper_queue=false) {
 
-  if (queue.length < BUFSIZE) queue.get_available_commands();
+  queue.get_available_commands();
 
   const millis_t ms = millis();