MKS H43 fixup (#21267)

Co-authored-by: makerbase <4164049@qq.com>
Co-authored-by: MKS-Sean <56996910+MKS-Sean@users.noreply.github.com>
Co-authored-by: Scott Lahteine <github@thinkyhead.com>

Marlin/src/gcode/queue.h

@@ -93,7 +93,9 @@ public:
 
     inline bool full(uint8_t cmdCount=1) const { return length > (BUFSIZE - cmdCount); }
 
-    inline bool empty() const { return length == 0; }
+    inline bool occupied() const { return length != 0; }
+
+    inline bool empty() const { return !occupied(); }
 
     inline CommandLine& peek_next_command() { return commands[index_r]; }
 
@@ -162,6 +164,11 @@ public:
    */
   static void advance();
 
+  /**
+   * Run the entire queue in-place
+   */
+  static void exhaust();
+
   /**
    * Add to the circular command queue the next command from:
    *  - The command-injection queue (injected_commands_P)