Patch long_move()

While the last move in the planner_buffer is running
it's duration is already subtracted from block_buffer_runtime_us.

Marlin/planner.h

 
     #if ENABLED(ENSURE_SMOOTH_MOVES)
       static bool long_move() {
-          if (blocks_queued()) {
+          if (blocks_queued() && block_buffer_runtime_us) {
             return block_buffer_runtime_us > (LCD_UPDATE_THRESHOLD) * 1000UL + (MIN_BLOCK_TIME) * 3000UL;
           }
           else