Avoid gcc waring:

../../../../ext/fox16_c/FXRuby.cpp: In function ‘VALUE FXRbConvertMessageData(FX::FXObject*, FX::FXObject*, FX::FXSelector, void*)’:
../../../../ext/fox16_c/FXRuby.cpp:578:17: warning: variable ‘fff’ set but not used [-Wunused-but-set-variable]
   FXInputHandle fff;
                 ^~~