FLTK: fix compile error

Author: chrisws

src/platform/fltk/runtime.h

@@ -25,6 +25,8 @@ struct Runtime : public System {
   void enableCursor(bool enabled);
   int handle(int event);
   void optionsBox(StringList *items);
+  void restoreWindowRect() {}
+  void saveWindowRect() {}
   MAEvent processEvents(int waitFlag);
   bool run(const char *bas) { return execute(bas); }
   void runSamples();