gvfs-tree: End GOptionEntry array with NULL
gvfs-tree: End GOptionEntry array with NULL

Prevent a segfault (revealed on OpenBSD) by null-terminating the
GOptionEntry array.

https://bugzilla.gnome.org/show_bug.cgi?id=727447

gicmo/gvfs,gicmo/gvfs,gicmo/gvfs,gicmo/gvfs