[glib: 1/2] docs: Clarify return/error behaviour of D-Bus signal subscriptions

[Philip Withnall <pwithnall src gnome org>]

commit c63d37fdc224920a13d0a6cb7787965e26009383
Author: Philip Withnall <withnall endlessm com>
Date:   Tue Nov 13 12:44:34 2018 +0000

    docs: Clarify return/error behaviour of D-Bus signal subscriptions
    
    Based on a patch by David Sommerseth, from
    https://gitlab.gnome.org/GNOME/glib/merge_requests/285/.
    
    Signed-off-by: Philip Withnall <withnall endlessm com>

 gio/gdbusconnection.c | 5 +++++
 1 file changed, 5 insertions(+)
---
diff --git a/gio/gdbusconnection.c b/gio/gdbusconnection.c
index 7270365b6..1f8a4695c 100644
--- a/gio/gdbusconnection.c
+++ b/gio/gdbusconnection.c
@@ -3410,6 +3410,11 @@ is_signal_data_for_name_lost_or_acquired (SignalData *signal_data)
  * signal is unsubscribed from, and may be called after @connection
  * has been destroyed.)
  *
+ * The returned subscription identifier is an opaque value which is guaranteed
+ * to never be zero.
+ *
+ * This function can never fail.
+ *
  * Returns: a subscription identifier that can be used with g_dbus_connection_signal_unsubscribe()
  *
  * Since: 2.26