Avoid 'g_type_init() is deprecated' warnings

Because of g_type_init we see the following:
clients/editor.c:1350:2: warning: ‘g_type_init’ is deprecated (declared
at /usr/include/glib-2.0/gobject/gtype.h:679)
[-Wdeprecated-declarations]

g_type_init() has been deprecated and does nothing
since version GLib 2.36.