Code review comment for lp://staging/~widelands-dev/widelands/fix_ui_bugs

Uos... just see this compiler warnings on trunk (which has this branch already in). I guess that those warnings are related to this branch:

../src/ui_basic/window.cc: In Elementfunktion »virtual bool UI::Window::handle_mousewheel(uint32_t, int32_t, int32_t)«:
../src/ui_basic/window.cc:402:41: Warnung: unverwendeter Parameter »which« [-Wunused-parameter]
 bool Window::handle_mousewheel(uint32_t which, int32_t x, int32_t y) {
                                         ^~~~~
../src/ui_basic/window.cc:402:56: Warnung: unverwendeter Parameter »x« [-Wunused-parameter]
 bool Window::handle_mousewheel(uint32_t which, int32_t x, int32_t y) {
                                                        ^
../src/ui_basic/window.cc:402:67: Warnung: unverwendeter Parameter »y« [-Wunused-parameter]
 bool Window::handle_mousewheel(uint32_t which, int32_t x, int32_t y) {