plugins: Fix usage of GST_GL_HAVE_WINDOW_* defines
plugins: Fix usage of GST_GL_HAVE_WINDOW_* defines

When these definitions are false, they are undef in the
preprocessor, not a defined value of 0. When they are unset the
compile fails with:

 'GST_GL_HAVE_WINDOW_WAYLAND' undeclared (first use in this function)

https://bugzilla.gnome.org/show_bug.cgi?id=780948

ceyusa/gstreamer-vaapi,GStreamer/gstreamer-vaapi,ceyusa/gstreamer-vaapi,GStreamer/gstreamer-vaapi