Improvement for ENSURE_SMOOTH_MOVES

Instead of waiting for a single long block, compare the complete block
buffer runtime for the long_move() check.

Marlin/stepper.cpp

@@ -1067,6 +1067,9 @@ void Stepper::finish_and_disable() {
 
 void Stepper::quick_stop() {
   cleaning_buffer_counter = 5000;
+  #if ENABLED(ENSURE_SMOOTH_MOVES)
+    planner.clear_block_buffer_runtime();
+  #endif
   DISABLE_STEPPER_DRIVER_INTERRUPT();
   while (planner.blocks_queued()) planner.discard_current_block();
   current_block = NULL;