fix: add missing CMD_UNDO and CMD_REDO cases inside switch block

Co-authored-by: aider (deepseek/deepseek-coder) <aider@aider.chat>

engine.c

@@ -487,8 +487,7 @@ void engine_process_commands(Engine *engine) {
                 atomic_store(&engine->transport_sample_position, 0);
                 break;
             }
-        }
+                
-        
             case CMD_UNDO:
                 engine_undo(engine);
                 break;