GdkFilterReturn is an enum defined in gdk/gdkevents.h, with
GDK_FILTER_CONTINUE=0, GDK_FILTER_TRANSLATE=1, and GDK_FILTER_REMOVE=2, so going
directly to bool rather than via

  ? GDK_FILTER_TRANSLATE : GDK_FILTER_CONTINUE

doesn't make a difference, and looks reasonable enough like it was the original
intent.

Change-Id: I0ae7a831d847c225c788cd0917f561fe119ccc22