gtk: fix scrolling in modal dialogs when event_widget is insensitive
gtk: fix scrolling in modal dialogs when event_widget is insensitive

When checking for modal grabs in gtk_main_do_event(), forward
GDK_SCROLL events to event_widget, even if it is insensitive.

johne53/MB3Gtk-2,johne53/MB3Gtk-2,Distrotech/gtk,Distrotech/gtk,Distrotech/gtk,johne53/MB3Gtk-2,johne53/MB3Gtk-2,johne53/MB3Gtk-2,Distrotech/gtk,Distrotech/gtk