fix tests to correctly construct a dummy Gtk.TargetEntry
fix tests to correctly construct a dummy Gtk.TargetEntry

* structs are sometimes a pain in gi.  Simply constructing them using the
   the standard constructor (e.g. Gtk.TargetEntry()) will malloc the struct
   but not correctly initialize the fields which can cause a crash.
 * tests didn't crash before because they were sending in bogus data that
   somehow did not trigger the issue
 * now with the C struct array marshallers doing the right thing, the incorrect
   use of TargetEntry was causing a crash

https://bugzilla.gnome.org/show_bug.cgi?id=627236

GNOME/pygobject,MathieuDuponchelle/pygobject,sfeltman/pygobject,choeger/pygobject-cmake,thiblahute/pygobject,thiblahute/pygobject,GNOME/pygobject,davibe/pygobject,thiblahute/pygobject,davibe/pygobject,pexip/pygobject,jdahlin/pygobject,choeger/pygobject-cmake,davidmalcolm/pygobject,sfeltman/pygobject,davibe/pygobject,davidmalcolm/pygobject,choeger/pygobject-cmake,davidmalcolm/pygobject,MathieuDuponchelle/pygobject,MathieuDuponchelle/pygobject,GNOME/pygobject,jdahlin/pygobject,pexip/pygobject,jdahlin/pygobject,sfeltman/pygobject,davibe/pygobject,pexip/pygobject