[geary] Fix warning/crash when libnotify enabled and server is not present. Bug 768911.

[Michael Gratton <mjog src gnome org>]

commit 8c22ce67270cc6e5f5401c48dda22a525e765a9b
Author: Michael James Gratton <mike vee net>
Date:   Mon Jul 18 13:51:40 2016 +1000

    Fix warning/crash when libnotify enabled and server is not present. Bug 768911.
    
    * src/client/notification/libnotify.vala (Libnotify): Allow for the
      server capabilities being null.

 bindings/vapi/libnotify.vapi           |    2 +-
 src/client/notification/libnotify.vala |   11 ++++++++---
 2 files changed, 9 insertions(+), 4 deletions(-)
---
diff --git a/bindings/vapi/libnotify.vapi b/bindings/vapi/libnotify.vapi
index c5a6751..163cff1 100644
--- a/bindings/vapi/libnotify.vapi
+++ b/bindings/vapi/libnotify.vapi
@@ -59,7 +59,7 @@ namespace Notify {
        [CCode (cheader_filename = "libnotify/notify.h")]
        public static unowned string get_app_name ();
        [CCode (cheader_filename = "libnotify/notify.h")]
-       public static GLib.List<string> get_server_caps ();
+       public static GLib.List<string>? get_server_caps ();
        [CCode (cheader_filename = "libnotify/notify.h")]
        public static bool get_server_info (out unowned string ret_name, out unowned string ret_vendor, out 
unowned string ret_version, out unowned string ret_spec_version);
        [CCode (cheader_filename = "libnotify/notify.h")]
diff --git a/src/client/notification/libnotify.vala b/src/client/notification/libnotify.vala
index bb25268..3f405e0 100644
--- a/src/client/notification/libnotify.vala
+++ b/src/client/notification/libnotify.vala
@@ -16,7 +16,7 @@ public class Libnotify : Geary.BaseObject {
     private Notify.Notification? error_notification = null;
     private Geary.Folder? folder = null;
     private Geary.Email? email = null;
-    private List<string> caps;
+    private List<string>? caps = null;
 
     public signal void invoked(Geary.Folder? folder, Geary.Email? email);
     
@@ -31,8 +31,10 @@ public class Libnotify : Geary.BaseObject {
         }
         
         init_sound();
-        caps = Notify.get_server_caps();
         
+        // This will return null if no notification server is present
+        this.caps = Notify.get_server_caps();
+
         monitor.new_messages_arrived.connect(on_new_messages_arrived);
     }
     
@@ -148,8 +150,11 @@ public class Libnotify : Geary.BaseObject {
         
     }
     
-    private Notify.Notification issue_notification(string category, string summary,
+    private Notify.Notification? issue_notification(string category, string summary,
         string body, Gdk.Pixbuf? icon, string? sound) {
+        if (this.caps == null)
+            return null;
+
         // Avoid constructor due to ABI change
         Notify.Notification notification = (Notify.Notification) GLib.Object.new(
             typeof (Notify.Notification),