gparam: Remove unsynchronized write to g_type field
gparam: Remove unsynchronized write to g_type field

GValue g_type field is used for synchronization with g_once_init_enter,
and so it should be written to only with g_once_init_leave.

Replace structure copy with memcpy that copies the one remaining field
of GValue, i.e., data array.

endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib